Carbon nanotubes - the promising adsorbent in wastewater treatment

A review on adsorption of heavy metals from wastewater using carbon nanotube and graphene-based nanomaterials

The rampant rise in world population, industrialization, and urbanization expedite the contamination of water sources. The presence of the non-biodegradable character of heavy metals in waterways badly affects the ecological balance. In this modern era, the unavailability of getting clear water as well as the downturn in water quality is a major concern. Therefore, the effective removal of heavy metals has become much more important than before. In recent years, the attention to better wastewater remediation was directed towards adsorption techniques with novel adsorbents such as carbon nanomaterials. This review paper primarily emphasizes the fundamental concepts, structures, and unique surface properties of novel adsorbents, the harmful effects of various heavy metals, and the adsorption mechanism. This review will give an insight into the current status of research in the realm of sustainable wastewater treatment, applications of carbon nanomaterials, different types of functionalized carbon nanotubes, graphene, graphene oxide, and their adsorption capacity. The importance of MD simulations and density functional theory (DFT) in the elimination of heavy metals from aqueous media is also discussed. In addition to that, the effect of factors on heavy metal adsorption such as electric field and pressure is addressed.

Magnetite Nanoparticles and Carbon Nanotubes for Improving the Operation of Mesophilic Anaerobic Digesters

Anaerobic waste processing contributes to the development of the bioenergy sector and solves environmental problems. To date, many technologies have been developed for increasing the rate of the anaerobic digestion process and yield of methane. However, new technological advancements are required to eliminate biogas production inefficiencies. The performance of anaerobic digesters can be improved by adding conductive materials. In this study, the effects of the separate and shared use of magnetite nanoparticles and carbon nanotubes in anaerobic digesters converting high-nitrogen-containing waste, chicken manure, were investigated. The tested nanomaterials accelerated the methane production and increased the decomposition of products from the acidogenesis and acetogenesis stages. The combined use of magnetite nanoparticles and carbon nanotubes gavae better results compared to using them alone or without them. Members of the bacterial classes Bacteroidia, Clostridia, and Actinobacteria were detected at higher levels in the anaerobic digesters, but in different proportions depending on the experiment. Representatives of the genera Methanosarcina, Methanobacterium, and Methanothrix were mainly detected within the methanogenic communities in the anaerobic digesters. The present study provides new data for supporting the anaerobic treatment of substrates with a high content of inhibitory compounds, such as chicken wastes.

Do Carbon Nanotubes and Asbestos Fibers Exhibit Common Toxicity Mechanisms?

During the last two decades several nanoscale materials were engineered for industrial and medical applications. Among them carbon nanotubes (CNTs) are the most exploited nanomaterials with global production of around 1000 tons/year. Besides several commercial benefits of CNTs, the fiber-like structures and their bio-persistency in lung tissues raise serious concerns about the possible adverse human health effects resembling those of asbestos fibers. In this review, we present a comparative analysis between CNTs and asbestos fibers using the following four parameters: (1) fibrous needle-like shape, (2) bio-persistent nature, (3) high surface to volume ratio and (4) capacity to adsorb toxicants/pollutants on the surface. We also compare mechanisms underlying the toxicity caused by certain diameters and lengths of CNTs and asbestos fibers using downstream pathways associated with altered gene expression data from both asbestos and CNT exposure. Our results suggest that indeed certain types of CNTs are emulating asbestos fiber as far as associated toxicity is concerned.

A state of the art overview of carbon-based composites applications for detecting and eliminating pharmaceuticals containing wastewater

The growing prevalence of new toxins in the environment continues to cause widespread concerns. Pharmaceuticals, organic pollutants, heavy metal ions, endocrine-disrupting substances, microorganisms, and others are examples of persistent organic chemicals whose effects are unknown because they have recently entered the environment and are displaying up in wastewater treatment facilities. Pharmaceutical pollutants in discharged wastewater have become a danger to animals, marine species, humans, and the environment. Although their presence in drinking water has generated significant concerns, little is known about their destiny and environmental effects. As a result, there is a rising need for selective, sensitive, quick, easy-to-handle, and low-cost early monitoring detection systems. This study aims to deliver an overview of a low-cost carbon-based composite to detect and remove pharmaceutical components from wastewater using the literature reviews and bibliometric analysis technique from 1970 to 2021 based on the web of science (WoS) database. Various pollutants in water and soil were reviewed, and different methods were introduced to detect pharmaceutical pollutants. The advantages and drawbacks of varying carbon-based materials for sensing and removing pharmaceutical wastes were also introduced. Finally, the available techniques for wastewater treatment, challenges and future perspectives on the recent progress were highlighted. The suggestions in this article will facilitate the development of novel on-site methods for removing emerging pollutants from pharmaceutical effluents and commercial enterprises.

Synthesis of Carbon Nanotubes (CNTs) from Poultry Litter for Removal of Chromium (Cr (VI)) from Wastewater

Pakistan, an agricultural country, raises 146.5 million commercial and domestic poultry birds, which generate around 544,831 tons of waste per year. This waste finds its final disposal in agricultural land as soil fertilizer or disposal site amendment. The usage of poultry litter for this purpose is uncontrolled, which results in environmental degradation such as emission of greenhouse gases, e.g., methane. However, alternative options such as thermochemical conversion of poultry litter can offer better solutions where this waste can be used as a low-cost carbon source for the synthesis of Multiwalled Carbon Nanotubes (MWCNTs). In this study, efforts were made to utilize this cheap and plentiful carbon source for the synthesis of CNTs in the presence of Ni/Mo/MgO as a catalyst, through pyrolysis. For a better yield of carbon product, the optimum ratio for the catalysts (Ni/Mo/MgO) was found to be 4:0.2:1. Furthermore, the process parameters were also optimized for better carbon yield. A good yield of CNTs resulted from a pyrolysis time of 12 min, a temperature of 825 °C, and a catalyst weight of 100 mg. The structure and morphology of the produced nanotubes were confirmed through X-ray Diffractometer (X-RD) and Scanning Electron Microscopy (SEM). The environmental application of the nanotubes was tested in a synthetic chromium solution in the lab using a batch experiment. Different experimental conditions (pH, adsorbent dosage, and contact time) were optimized to improve the adsorption of Cr (VI) by carbon nanotubes and a UV-Visible spectrophotometer was used at 540 nm to measure the absorbance of Cr (VI). The results showed that up to 81.83% of Cr (VI) removal was achieved by using 8 mg of CNTs at pH 3 with 400 rpm at 180 min of contact time. Thus, it was concluded that poultry litter can be a useful source for the synthesis of MWCNTs and thereby removal of Cr (VI) from industrial tanneries' wastewater.

Developments in the Application of Nanomaterials for Water Treatment and Their Impact on the Environment

Nanotechnology is an uppermost priority area of research in several nations presently because of its enormous capability and financial impact. One of the most promising environmental utilizations of nanotechnology has been in water treatment and remediation where various nanomaterials can purify water by means of several mechanisms inclusive of the adsorption of dyes, heavy metals, and other pollutants, inactivation and removal of pathogens, and conversion of harmful materials into less harmful compounds. To achieve this, nanomaterials have been generated in several shapes, integrated to form different composites and functionalized with active components. Additionally, the nanomaterials have been added to membranes that can assist to improve the water treatment efficiency. In this paper, we have discussed the advantages of nanomaterials in applications such as adsorbents (removal of dyes, heavy metals, pharmaceuticals, and organic contaminants from water), membrane materials, catalytic utilization, and microbial decontamination. We discuss the different carbon-based nanomaterials (carbon nanotubes, graphene, graphene oxide, fullerenes, etc.), and metal and metal-oxide based nanomaterials (zinc-oxide, titanium dioxide, nano zerovalent iron, etc.) for the water treatment application. It can be noted that the nanomaterials have the ability for improving the environmental remediation system. The examination of different studies confirmed that out of the various nanomaterials, graphene and its derivatives (e.g., reduced graphene oxide, graphene oxide, graphene-based metals, and graphene-based metal oxides) with huge surface area and increased purity, outstanding environmental compatibility and selectivity, display high absorption capability as they trap electrons, avoiding their recombination. Additionally, we discussed the negative impacts of nanomaterials such as membrane damage and cell damage to the living beings in the aqueous environment. Acknowledgment of the possible benefits and inadvertent hazards of nanomaterials to the environment is important for pursuing their future advancement.

The Application of Carbon Nanotube/Graphene-Based Nanomaterials in Wastewater Treatment

The treatment of organic wastewater is of great significance. Carbon nanotube (CNT)/graphene-based nanomaterials have great potential as absorbent materials for organic wastewater treatment owing to their high specific surface area, mesoporous structure, tunable surface properties, and high chemical stability; these attributes allow them to endure harsh wastewater conditions, such as acidic, basic, and salty conditions at high concentrations or at high temperatures. Although a substantial amount of work has been reported on the performance of CNT/graphene-based nanomaterials in organic wastewater systems, engineering challenges still exist for their practical application. Herein, the adsorption mechanism of CNT- and graphene-based nanomaterials is summarized, including the adsorption mechanism of CNTs and graphene at the atomic and molecular levels, their hydrophilic and hydrophobic surface properties, and the structure-property relationship required for adsorption to occur. Second, the structural modification and recombination methods of CNT- and graphene-based adsorbents for various organic wastewater systems are introduced. Third, the engineering challenges, including the molding of macroscopically stable adsorbents, adsorption isotherm models and adsorption kinetic behaviors, and reversible adsorption performance compared to that of activated carbon (AC) are discussed. Finally, cost issues are discussed in light of scalable and practical application of these materials.

Efficient Removal of Pb(II) from Aqueous Solutions by Using Oil Palm Bio-Waste/MWCNTs Reinforced PVA Hydrogel Composites: Kinetic, Isotherm and Thermodynamic Modeling

Polyvinyl alcohol (PVA) hydrogel are still restricted for some applications because their lower mechanical strength and thermal stability. The PVA-based composites are drawing attention for the removal of heavy metals based on their specific functionality in adsorption process. The main objective of this work is to synthesize oil palm bio-waste (OPB)/multiwalled carbon nanotubes (MWCNTs) reinforced PVA hydrogels in the presence of N,N′-methylenebisacrylamide (NMBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator via simple in-situ polymerization technique. The as-prepared reinforced nanocomposites were characterized by FESEM, BET surface area, differential scanning calorimetry (DSC), TGA and FTIR analysis. The possible influence of OPB and MWCNTs on the tensile strength, elongation at break and elastic modulus of the samples were investigated. It was found that reinforced nanocomposites exhibited enhanced mechanical properties as compared to non-reinforced material. The evaluation of reinforced nanocomposites was tested by the removal of Pb(II) aqueous solutions in a batch adsorption system. The pseudo-second-order kinetic model was used to illustrate the adsorption kinetic results and Langmuir isotherm was more suitable to fit the equilibrium results providing maximum adsorption capacities. The evaluation of thermodynamic parameters describes the spontaneous, endothermic and chemisorption adsorption process while activation energy reveals the physical adsorption mechanism. Therefore, the coordination effects among OPB, MWCNTs and PVA polymer hydrogels can produce a promising adsorbent material for wastewater treatment applications.

Use of nanohybrid nanomaterials in water treatment: highly efficient removal of ranitidine

Entire elimination of pharmaceutical drugs from waste- and domestic-waters has attracted great attention due to their potent adverse effects on human health, particularly the human immune system. Many risks have been related to the presence of different types of drugs at different concentrations in wastewater. These risks include antimicrobial resistance (AMR), endocrine action, hormonal activation of cancers, and photodegradation of drugs. In this study, new nanohybrid materials consisting of graphene oxide (GO) and oxidized carbon nanotubes (OCNTs) were developed to remove a well-known drug, namely, ranitidine that treats stomach ulcers and gastrointestinal (GI) reflux disease from aqueous solutions. The characterization of synthesized nanohybrid GO-OCNTs was performed using spectroscopic (FTIR, and XRD), thermogravimetric (TGA) and microscopic (SEM) techniques. Batch adsorption experiments were used to investigate the technical feasibility of using synthesized GO-OCNTs for the removal of ranitidine from aqueous solutions. The effects of different operating conditions such as contact time, nanohybrid mass, solution temperature, solution pH, % crosslinking agent, and GO-to-OCNT ratio on the entire elimination of ranitidine were investigated. The experimental results indicated that the removal of ranitidine was very efficient, where 98.3% removal of the drug from aqueous solutions was achieved with a drug uptake of 97.8 mg g⁻¹. Moreover, the results indicated the optimum conditions for the removal of ranitidine, which are as follows: contact time = 140 minutes, nanohybrid GO-OCNT mass = 10 mg, solution temperature = 290 K, solution pH = 6.4, % crosslinking agent = 0.5%, and GO to O-CNT ratio = 1 : 4. The equilibrium data were fitted to different adsorption isotherms and Langmuir was found to best describe our data. Dynamic studies demonstrated that ranitidine adsorption followed pseudo-second order, and the thermodynamic parameters confirmed exothermic drug adsorption as well as the physisorption process.

Entire elimination of pharmaceutical drugs from waste- and domestic-waters has attracted great attention due to their potent adverse effects on human health, particularly the human immune system.

Solvent-free production of nano-FeS anchored graphene from Ulva fasciata: A scalable synthesis of super-adsorbent for lead, chromium and dyes

Here we demonstrate, a simple and solvent-free synthetic route for the production of FeS/Fe(0) functionalized graphene nanocomposite (G-Fe) via a one-step pyrolysis of seaweed biomass (Ulva fasciata). It is proposed that the natural abundance of both inorganic and organic sulfur in the seaweed induces the reduction of exfoliated graphitic sheets at elevated temperatures. FeCl₃ was employed both as the iron precursor as well as the templating agent. Iron doping played a dual-faceted role of exfoliating as well as activating agent, producing composite with high adsorption capacity for Pb²⁺ (645 ± 10 mg/g), CR (970 mg/g), CV(909 mg/g), MO (664 mg/g), MB (402 mg/g) dyes and good recyclability (8 cycles). Pb²⁺ adsorption was irreversible even at low pH values and the spent composite (G-Fe-Pb) was utilized for efficient Cr(IV) removal (̴100 mg/g). The adsorption data followed the pseudo second order kinetics while the equilibrium data fitted perfectly into the Langmuir adsorption equation. Further, a thin layer of composite was deposited on a filter paper by vacuum filtration which was tested under continuous filtration mode for RB5 dye removal. Preliminary results highlight the potential of this composite to be used in pretreatment steps in hybrid membrane processes for filtration of complex wastewater feeds.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of small volatile molecules using a parylene-matrix chip

RATIONALE

In matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS), volatile small molecules have been nearly impossible to analyze because (1) such molecules evaporate under drying and vacuum conditions and (2) the organic matrix creates matrix peaks in the low mass-to-charge (m/z) range (m/z <500). In this work, the analysis of volatile small molecules using MALDI-TOFMS was realized using (1) a parylene-matrix chip to eliminate the matrix peaks of the organic matrix and (2) graphene for the effective adsorption of the small volatile molecules.

METHODS

The parylene-matrix chip was produced by deposition of a partially porous parylene-N thin film on a dried organic matrix array. The sample solution of volatile small molecules was mixed with the graphene and then placed on the parylene-matrix chip for MALDI-TOFMS. Analogs of chemical agents called dimethyl methyl phosphonate (DMMP) and 2-chloroethylethylsulfide (CEES) were used as model compounds for the small volatile molecules, and the sensing parameters were estimated, such as the limit of detection (LOD) and the detection range.

RESULTS

MALDI-TOFMS based on the parylene-matrix chip and graphene as the adsorbent could achieve a LOD of approximately 1 ppb in the detection range of 1 ppm-1 ppb for the highly volatile DMMP and CEES.

CONCLUSIONS

The parylene-matrix chip with graphene can be applied for the detection of volatile small molecule analytes in the m/z ratio range of small molecules (m/z <500) using graphene as an effective adsorbent.

Isotherm, thermodynamic, kinetics, and adsorption mechanism studies of Ethidium bromide by single-walled carbon nanotube and carboxylate group functionalized single-walled carbon nanotube

The studies of kinetics and thermodynamics of adsorption of Ethidium bromide in aqueous solutions on single-walled carbon nanotube (SWCNT) and carboxylate group functionalized single-walled carbon nanotube (SWCNT-COOH) surfaces were by UV-Vis spectroscopy. The adsorption kinetics for SWCNT-COOH and SWCNTs were well described by a intra-particle diffusion model, while Langmuir, Freundlich, Harkins-Jura, and Halsey isotherms described the adsorption isotherms, and the adsorption thermodynamic parameters of equilibrium constant (K0), standard free energy (ΔG0), standard enthalpy (ΔH0), and standard entropy changes (ΔS0) were measured. The maximum surface coverage for SWCNTs is 36.10% and for SWCNT-COOH is 38.42%. The values of ΔH0 and ΔG0 suggested that the adsorption of EtBr on SWCNT-COOH and SWCNTs was endothermic and spontaneous. The adsorption of EtBr on SWCNT-COOH is more than SWCNTs surfaces.

Human health effects of residual carbon nanotubes and traditional water treatment chemicals in drinking water

The volume of industrial and domestic wastewater is increasing significantly year by year with the change in the lifestyle based on mass consumption and mass disposal brought about by the dramatic development of economies and industries. Therefore, effective advanced wastewater treatment is required because wastewater contains a variety of constituents such as particles, organic materials, and emulsion depending on the resource. However, residual chemicals that remain during the treatment of wastewaters form a variety of known and unknown by-products through reactions between the chemicals and some pollutants. Chronic exposure to these by-products or residual chemicals through the ingestion of drinking water, inhalation and dermal contact during regular indoor activities (e.g., showering, bathing, cooking) may pose cancer and non-cancer risks to human health. For example, residual aluminium salts in treated water may cause Alzheimer's disease (AD). As for carbon nanotubes (CNTs), despite their potential impacts on human health and the environment having been receiving more and more attention in the recent past, existing information on the toxicity of CNTs in drinking water is limited with many open questions. Furthermore, though general topics on the human health impacts of traditional water treatment chemicals have been studied, no comparative analysis has been done. Therefore, a qualitative comparison of the human health effects of both residual CNTs and traditional water treatment chemicals is given in this paper. In addition, it is also important to cover and compare the human health effects of CNTs to those of traditional water treatment chemicals together in one review because they are both used for water treatment and purification.

Removal of organic compounds from water by using a gold nanoparticle-poly(dimethylsiloxane) nanocomposite foam

A low density, highly compressible, porous foam of poly(dimethylsiloxane) (PDMS) incorporated with Au nanoparticles (10-50 nm) has been synthesized by using a single-step process with water as a medium. It exhibits high swelling ability (≈600%) against benzene, toluene, ethylbenzene, and xylene (BTEX)-a property that has been exploited in the removal of oil spills from water. It is resistant to harsh chemical environments. It is also effective against odorous sulfur containing contaminants such as thioanisole. It works repeatedly and efficiently over many cycles. The regeneration of the foam is rather simple: heating in air to 300 °C for short time brings back its original activity. The fascinating properties of Au nanoparticles could be mingled with those of PDMS to provide a sustainable and practical solution for water treatment. It is also demonstrated to work effectively for deodorizing garlic extract with a promise as a food packaging material.