The pH-dependent adsorption of ibuprofen (IBP) onto acid-functionalized multiwalled carbon nanotubes (CNT-COOH) was investigated by batch adsorption experiments and quantum mechanics (QM) and ...molecular mechanics (MM) simulation. A force field was developed and applied for monitoring interactions between IBP and CNT-COOH. Our simulations relied on the behavior of the pH-sensitive CNT-COOH functional groups and IBP molecules in solution, which occur as neutral or deprotonated species. QM and MM calculations were performed to determine the pH-dependent binding energy (E BE pH), and molecular dynamics (MD) simulations were performed to calculate the number of IBP species that interact with the CNT surfaces at different pH conditions. The adsorption experiments demonstrated the strong affinity of IBP for CNT-COOH in acidic conditions, but a much decreased adsorption under basic conditions. The QM and MM results agreed with the experiments and further demonstrated that the E BE pH values were attractive in acidic conditions, but repulsive in neutral and basic conditions. The MD results revealed that the largest number of IBP species interacted with CNT-COOH in acidic conditions, where hydrogen bonds were observed. In basic conditions, the deprotonated species of both the CNTs and IBP bind via sodium ion mediation. Hydrogen bonding and ion mediation accounted for a small fraction of the total binding, whereas hydrophobic interactions were responsible for most of the adsorption across the pH range. There is an increase in electrostatic repulsion as the system becomes more basic when the greatest numbers of negatively charged deprotonated groups on both the CNTs and IBP occur. Our study provides valuable insight into pH-dependent binding and will aid in the design of more efficient nanomaterials for water remediation and drug delivery.
In recent years, carbon-based materials, particularly carbon nanotubes (CNTs), have gained intensive research attention in the fabrication of organic solar cells (OSCs) due to their outstanding ...physicochemical properties, low-cost, environmental friendliness and the natural abundance of carbon. In this regard, the low sheet resistance and high optical transmittance of CNTs enables their application as alternative anodes to the widely used indium tin oxide (ITO), which is toxic, expensive and scarce. Also, the synergy between the large specific surface area and high electrical conductivity of CNTs provides both large donor-acceptor interfaces and conductive interpenetrating networks for exciton dissociation and charge carrier transport. Furthermore, the facile tunability of the energy levels of CNTs provides proper energy level alignment between the active layer and electrodes for effective extraction and transportation of charge carriers. In addition, the hydrophobic nature and high thermal conductivity of CNTs enables them to form protective layers that improve the moisture and thermal stability of OSCs, thereby prolonging the devices' lifetime. Recently, the introduction of CNTs into OSCs produced a substantial increase in efficiency from ∼0.68 to above 14.00%. Thus, further optimization of the optoelectronic properties of CNTs can conceivably help OSCs to compete with silicon solar cells that have been commercialized. Therefore, this study presents the recent breakthroughs in efficiency and stability of OSCs, achieved mainly over 2018-2021 by incorporating CNTs into electrodes, active layers and charge transport layers. The challenges, advantages and recommendations for the fabrication of low-cost, highly efficient and sustainable next-generation OSCs are also discussed, to open up avenues for commercialization.
Since the 1970s, palladium-catalysed carbon–carbon (C–C) bond formation has made a critical impact in organic synthesis. In early studies, homogeneous palladium catalysts were extensively used for ...this reaction with limitations such as difficulty in separation and recycling ability. Lately, heterogeneous palladium-based catalysts have shown promise as surrogates for conventional homogeneous catalysts in C–C coupling reactions, since the product is easy to isolate, while the catalyst is reusable and hence sustainable. Recently, a better part of these heterogeneous palladium catalysts are supported on carbon nanotubes (Pd/CNTs), that have shown superior catalytic performance and better recyclability since the CNT support imparts stability to the palladium catalyst. This review discusses the wide variety of surface functionalization techniques for CNTs that improve their properties as catalyst supports, as well as the methods available for loading the catalyst nanoparticles onto the CNTs. It will survey the literature where Pd/CNTs catalysts have been utilized for C–C coupling reactions, with particular emphasis on Suzuki–Miyaura and Mizoroki–Heck coupling reactions. It will also highlight some of the important parameters that affect these reactions.
Workplace exposure to persistent organic pollutants is a concern for human health. This study examined the presence of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in ...the indoor dust from two major e-waste recycling sites and a university electronic equipment repair workshop in Durban, South Africa, in order to evaluate the implication of dust for occupational exposure. The mean ∑
(
n
= 8)
PBDEs and ∑
(
n
= 3)
PCBs were 20,094 and 235 ng g
−1
, respectively. The levels of PBDEs and PCBs obtained in one of the recycling sites (123–27,530 and 161–593 ng g
−1
) were significantly higher than the levels obtained (91–7686 and <DL–42 ng g
−1
, respectively) in the same site after site cleanup/maintenance. Occupational exposure was assessed for different exposure scenarios by using the 5th and 95th percentile, and the median and mean concentrations measured at the sites. By assuming a mean and a high dust intake rate, the average and 95th percentile daily exposure doses (∑DED/ng kg
−1
bw day
−1
) of PBDEs were 3.98, 8.52 and 7.58, 16.19, respectively, and of PCBs were 0.047, 0.094 and 0.089, 0.179, respectively. The ∑DEDs of PBDEs and PCBs were lower than the reference (RfD) values for BDE 47, BDE 99, BDE 153 and BDE 209, and Aroclor 1254 and 1016. Nevertheless, continual exposure to high levels of these pollutants is a concern; but as shown, the exposure can be significantly reduced if the e-waste facilities are cleaned thoroughly regularly.
Estimation of community-wide consumption of illicit drugs through wastewater analysis is a new concept in Africa although widely applied in developed nations as wastewater-based epidemiology (WBE). ...It is an important tool that can be used in understanding supply and demand patterns of illicit drug use on a local, national, and international scale. Information on illicit drug use is currently limited in Africa, because of a lack of monitoring structures by governments and financial constraints. This study hopes to bridge that gap by contributing to Africa's baseline information on illicit drug use. This study provides the first application of wastewater analysis to quantitatively evaluate daily illicit drug use in the eThekwini Metropolitan Municipality of KwaZulu-Natal Province of South Africa by quantifying the major urinary excreted metabolites, called drug target residues (DTRs), in raw wastewater from four major wastewater treatment plants (WWTPs) sampled for a week. The results showed that cocaine was the dominant illicit drug consumed in the catchment followed by amphetamine, methamphetamine, 3,4-methylenedioxymethamphetamine and 3,4-methylenedioxyamphetamine, with a per capita use of 360–3000 mg day−1 1000 inh−1, 47–800 mg day−1 1000 inh−1, 19–120 mg day −1 1000 inh−1, not detected (ND) to 4.9 mg day−1 1000 inh−1, and ND to 410 g day−1 1000 inh−1 respectively. The weekly usage patterns between the four WWTPs differed probably due to the lifestyle of the populace serving the different WWTPs. These results provide useful data on illicit drug use in eThekwini that can be utilised by public health agencies to implement suitable response strategies.
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•Illicit drug consumption was estimated from eThekwini wastewaters in South Africa.•Amphetamine, cocaine and methamphetamine were the most consumed.•Heroin and methylenedioxypyrovalerone were not detected.•Wastewater-based epidemiology is advocated to monitor illicit drug use in Africa.
The use of urine-derived fertilizers has several economic and environmental advantages. However, there is concern that pharmaceutical residues present in urine could enter the food chain after plant ...uptake and pose potential risks to human and animal health. A pot experiment was conducted to evaluate the uptake of nine target antiretroviral drugs (ARVDs) by pepper (Capsicum annum), ryegrass (Lolium perenne) and radish (Raphanus sativus) grown in two soils of contrasting texture and organic matter content and fertilized with stored urine, nitrified urine concentrate (NUC), and struvite. Nevirapine was the only ARVD detected in crops grown with NUC and struvite on both soils, but the concentrations were below the limit of quantification. Plants fertilized with stored urine absorbed lamivudine, ritonavir, stavudine, emtricitabine, nevirapine, and didanosine, while abacavir, efavirenz and zidovudine were not detected. The ARVDs detected in the soils after harvest were significantly higher in the soil with high organic matter and clay content. To assess direct human exposure the estimated daily dietary intake (DDI) of ARVDs by consumption of the pepper and radish fertilized with stored urine was compared with the Threshold of Toxicological Concern (TTC) values based on the Cramer classification tree. The calculated DDI values for all ARVDs were about 300–3000 times lower than the TTC values for class III compounds. Therefore, daily consumption of these crops fertilized with stored urine does not pose a health risk to the consumer. Future research is required to assess the impact of ARVD metabolites, which may be more harmful to human health than the parent compounds.
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•Plants fertilized with stored urine absorbed six of the nine target ARVDs.•Nevirapine was the only ARVD detected in crops grown with nitrified urine and struvite.•The ARVDs detected in the soils were significantly higher in the soil with high organic matter and clay content.•Daily consumption of crops fertilized with stored urine does not pose a health risk to the consumer.
The formation of corrosive sulfur as a result of the addition of dibenzyl disulfide (DBDS) to transformer oils has been investigated. Corrosive sulfur in a transformer affects all aspects of its ...insulation and conductive components by deposition of Cu2S. Previous studies have suggested that the formation of Cu2S was initiated by a DBDS–Cu complex. This work shows an alternate pathway via thiolate formation for the deposition of corrosive sulfur on copper conductors. The open circuit potential results showed no reduction of DBDS onto copper surfaces, but the degradation products of DBDS, which include dibenzyl sulfide and benzyl mercaptan, were both found to adsorb on copper surfaces, forming a copper thiolate. The formation of copper thiolates was also demonstrated by a heterogeneous reaction of CuO and benzyl mercaptan. Thermal degradation of the thiolate eventually produced copper sulfide Cu7.2S4 as identified by X-ray diffraction analysis.
The efficiency of adsorption of rhodamine B (RhB) from aqueous solution was investigated through a series of batch experiments by using cobalt ferrite nanoparticles (CoFe
2
O
4
), acid-functionalized ...multiwalled carbon nanotubes (MWCNT-COOH) and carbon nanotube-cobalt ferrite nanocomposites. The adsorption capacity was evaluated as a function of pH, contact time, adsorbent dose, dye concentration and temperature. The effect of increasing the percentage of MWCNT-COOH in the nanocomposites was also studied. The adsorption capacity was lowest in CoFe
2
O
4
(5.165 mg g
−1
) and highest with MWCNT-COOH (42.68 mg g
−1
). For the nanocomposites, the adsorption capacity was enhanced with an increase in the amount of MWCNT-COOH. The optimum pH for adsorption was observed at 7 at which equilibrium was reached after 360 min. The kinetics of adsorption was fitted to the pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion models. The results showed that the pseudo-second order model best described the data as reflected in the lowest value for the sum of squared residuals. Among the various adsorption isotherms tested, the Langmuir isotherm provided the best fit to the equilibrium data. The thermodynamic parameters, Δ
H
°, Δ
S
° and Δ
G
°, were obtained over a temperature range of 20-45 °C. Adsorption was spontaneous, endothermic and entropy-driven, except for one of the doped nanocomposites for which adsorption was exothermic. A good desorption of RhB from the loaded adsorbents was obtained by using either acetone or ethanol with a desorption efficiency in the range of 62-95%.
Magnetic cobalt ferrite-carbon nanotube nanocomposites are effective and reusable adsorbents for remediation of wastewaters contaminated with dyes.
Amino-acyl-quinoxalinone yellow dyes are cyclised analogues of the yellow azomethine dyes developed for, and still used in, silver halide colour photography. Unlike image azomethine dyes, which are ...rapidly deactivated in their excited states by torsion about the azomethine bond, amino-acyl-quinoxalinone dyes have an interesting photophysics because torsion is not possible due to their cyclised structure. We report results from studies on singlet and triplet state properties, and singlet oxygen yields, of the yellow dye, 7-diethylamino-3-(2,2-dimethyl-propionyl)-5-methyl-1-phenyl-1
H
-quinoxalin-2-one, in polar and nonpolar solvents. The dye photophysics is characterised by a weak fluorescence, with a solvent dependent emission yield (Φ
F
≈ 0.002–0.004), and short singlet state lifetime (τ
expt
≈ 20–50 ps), both increasing by a factor of ≈2 in going from polar acetonitrile to non-polar dioxane as solvent. DFT ZINDO calculations show a transition involving significant electron transfer from the diethyl-amino group into the carbonyl region of the molecule. In solution, in the presence of oxygen, the triplet state decays almost exclusively by oxygen quenching, and singlet oxygen is produced in high yield (Φ
∆
≈ 0.5–0.55). The triplet state absorbs across the 450–750 nm region with maxima around 480 and 650 nm, and moderate molar absorption coefficients (ca. 6000–8000 M
−1
cm
−1
). In a glass at 77 K, triplet decay gives a red phosphorescence, with λ
max
≈ 640–650 nm, and a ≈ 0.25 s lifetime. If singlet oxygen yields are a good indication of triplet yields, then internal conversion and intersystem crossing occur with roughly equal efficiency.
The nitrogen-functionalized multiwalled carbon nanotubes synthesized proved effective and efficient for the adsorption of Pb2+ and Zn2+ from aqueous solutions.
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...•Nitrogen-functionalized carbon nanotubes are efficient for Pb2+ and Zn2+ removal.•Kinetic, isotherm and thermodynamics of adsorption were determined.•Adsorption results were supported by DFT calculations.•Metal ions can be desorbed for reuse and the sorbent regenerated.
The ligand, 4′-(4-hydroxyphenyl)-2,2′:6′,2″-terpyridine, was bonded to multiwalled carbon nanotubes to afford nitrogen-functionalized carbon nanotubes (MWCNT-ttpy). This material was compared with acid-functionalized multiwalled carbon nanotubes (MWCNT-COOH) for the removal of Pb2+ and Zn2+ from aqueous solution. The comparison was conducted both experimentally and theoretically by means of batch adsorption experiments and density functional theory (DFT) analysis, respectively.
The adsorption capacities (qe) of the adsorbents increased with increasing pH, contact time and adsorbent dose. The adsorption of Pb2+ and Zn2+ onto both sorbents was conducted at an optimum pH of 4.5 and 5.5, respectively. For both metal ions, better removal was observed with MWCNT-ttpy than with MWCNT-COOH. In the case of Pb2+, the Langmuir maximum adsorption capacity (qm) increased from 20.60 to 36.23mgg−1, and for Zn2+, qm increased from 18.51 to 32.60mgg−1, in going from MWCNT-COOH to MWCNT-ttpy, respectively. DFT analysis supports the experimental results showing a better coordination of Pb2+ to the nitrogen-donor atoms on MWCNT-ttpy than for Zn2+. The pseudo-second order kinetics model fitted both systems well, indicating a bimolecular interaction between the adsorbate cations and sorbents. The adsorption processes were endothermic in nature and spontaneous. DFT studies reveal that the metal-adsorbent interactions proceeded via a coordination/electrostatic mechanism between the nitrogen/oxygen donor atoms contained in the adsorbents and the metal ions. Desorption studies showed high desorption efficiencies, thereby demonstrating the suitability of the adsorbents for reuse.
Thus, nitrogen-functionalized carbon nanotubes show promise as a good reusable adsorbent for the removal of Pb2+ and Zn2+ from wastewaters.
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