We herein report the optimization and application of silver cationization (Ag
+
) in combination with laser desorption ionization (LDI) ultrahigh-resolution mass spectrometry (UHR-MS) to determine ...the structures of the sulfur-containing compounds present in heavy crude oil. A number of sulfur-containing model compounds were used to optimize the positive-ion mode LDI-MS conditions in the presence of a silver-complexing agent. Under the optimized LDI conditions, sulfur-rich heavy oil fractions were treated with the silver salt, where Ag
+
coordinated with the sulfur atoms to speciate the sulfur species. The obtained results suggested that benzothiophenic, naphtheno-non-aromatic sulfides, and non-aromatic thiols were the major components present in the analyzed oil sample.
Graphical abstract
Solar-assisted photocatalytic degradation of organic pollutants has emerged as efficient technology for the effective treatment of industrial wastewater. Here, we report a simple technique for the ...fabrication of a novel ternary photocatalyst from kaolinite (K),
TiO
2
(T) and ZnO (Z). The most efficient catalyst was prepared at a calcination temperature of
600
∘
C
. The fabricated ternary composite was characterized using different analytical techniques including Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, field emission-scanning electron microscopy and energy dispersive X-ray spectroscopy. The photocatalytic degradation was performed at room temperature (
25
∘
C
) using Remazol Red (RR), an anionic azo dye, as the model compound. A maximum of 98% degradation of RR was found with the ternary catalyst
K
0.50
T
0.45
Z
0.05
, which was prepared from 50% kaolinite (w/w), 45%
TiO
2
(w/w) and 5% ZnO (w/w). The catalyst was found to be suitable for long-term repeated applications. Mechanistic investigation through radical trapping experiments confirmed hydroxyl radicals as the potential contributor to the photocatalytic degradation of RR. It is highly expected that a novel photocatalyst design such as this will pave way towards further development of materials capable of hazardous dye removal from industrial effluents.
This study attempted to harness the dual benefit of adsorption and photocatalytic degradation for efficiently removing a model anionic azo dye, Orange G, from an aqueous solution. For this purpose, a ...series of bifunctional nanohybrids containing different proportions of naturally occurring biopolymer chitosan and ternary photocatalyst made of kaolinite, TiO2, and ZnO were prepared through the dissolution of chitosan in acid and subsequent deposition on ternary photocatalyst. The characterization through Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectrum (EDS) have confirmed the successful fabrication of nanohybrids from TiO2 and chitosan. The adsorptive separation of Orange G from the aqueous solution and subsequent degradation under solar irradiation was thoroughly studied by recording the λmax value of dye in the ultraviolet–visible (UV-Vis) spectrophotometer at various operating conditions of pH, dye concentration, contact time, and compositional variation. The nanohybrid (TP0.75CS0.25) fabricated from 75% ternary photocatalyst (w/w) and 25% chitosan (w/w) removed 97.4% Orange G within 110 min at pH 2.5 and 10 mg/L dye concentration. The relative contribution of chitosan and ternary composite on dye removal was understood by comparing the experimental results in the dark and sunlight. Recyclability experiments showed the suitability of the nanohybrid for long-term repeated applications. Equilibrium experimental data showed a better correlation with the Langmuir isotherm and pseudo-second-order kinetic model. The rapid and nearly complete removal capacity, long-term reusability, and simple fabrication technique make this novel nanohybrid a promising advanced material for removing hazardous azo dyes from industrial effluents.
Nitrogen-doped carbon catalysts prepared from amino-functionalized metal–organic frameworks amino-MIL-101(Al) were investigated for the oxygen-reduction reaction (ORR) with special emphasis on ...elucidating the role of different nitrogen species (e.g., pyridinic, pyrrolic, and quaternary N) as active catalytic sites. Careful optimization of pyrolysis temperature of the amino-MIL-101(Al) leveraged the synthesis of the catalysts with or without quaternary N functionalities. This allowed us to investigate the type(s) of N species responsible for the ORR catalysis and thus address the conflicting results reported so far regarding the pyridinic and/or quaternary N as active sites for ORR catalysis via four-electron transfer (4e–) pathways. Our findings suggest that the total nitrogen content in the catalysts does not influence the ORR, while the quaternary N sites exclusively catalyze the reduction of O2 via the 4e– transfer pathway in both alkaline and acidic electrolytes. Catalysts containing only pyridinic and pyrrolic N were observed to be ineffective for the ORR. The experimental results were further supported by computational simulation using the gradient–correlated density functional theory which revealed that the dissociative O2 adsorption (i.e., binding and cleavage of OO bonds) is more favorable to quaternary N. Furthermore, calculations based on the relative surface potential energy, dipole moment, binding energy, and electron density indicate that the most stable structure of O2 chemisorption sites could only be achieved on the quaternary N carbon.
This study was adopted to investigate the removal of Cr(III)and other physicochemical parameters of chrome tan wastewater. For this purpose, three precipitating agents, CaCO3, NaHCO3, and MgO, were ...used to treat chrome tan wastewater. After treatment, it was found, in three different dose trials, that each agent removed almost 97-99.5 % of chromium. At the same time, it was observed that with the increase of doses, removal percentage of TDS, conductivity, and turbidity of effluent were reduced. In the case of NaHCO3 and CaCO3, Cr(III) removal percentage at optimum pH was found to be 99.97% and 99.95% respectively, whereas the maximum removal percentage for MgO was found to be 99.98%. The NaHCO3 and CaCO3 were found to be comparable to MgO for Cr(III) removal from chrome tan wastewater. The recovered chromium concentration in the sludge for NaHCO3 and CaCO3 were also similar to that of MgO. This research suggests that these two precipitating agents can be used in the same way as MgO, for Cr removal and recovery treatments. Moreover, this recovered chromium can be reused, thus reducing the environmental pollution.
Advanced engineering of naturally occurring materials opens new doors in nanoscience and nanotechnology for the separation and/or removal of environmental hazards. Here, a series of nanocomposites ...containing kaolinite and chitosan varying in the range of 20 to 80% (w/w) kaolinite were used for the adsorptive removal of a reactive textile dye, Remazol Red, from an aqueous solution. Batch experiments were carried out to investigate the effects of pH, contact time, and initial dye concentration on the adsorption capacity. Nanocomposites containing 80% kaolinite (w/w) and 20% chitosan (w/w), i.e., NK80C20, showed an equilibrium adsorption capacity of 371.8 mg/g at pH 2.5, which was 5.2 times higher than that of commercial activated charcoal. Moreover, NK80C20 was regenerated instantly up to 99.9% at pH 10. Therefore, NK80C20 can be effectively utilized as a potential adsorbent for the separation of Remazol Red and homologous azo dyes from industrial effluents. We expect that the findings from this study will play a vital role in environmental research leading to advanced applications in water purification.
Heavy-metal pollution of surface water, sediment and fish have been seen as a major global problem, with a significant proportion of developing countries like Bangladesh. This study assessed the ...intensity of alarming six toxic substances (Cr, Zn, Fe, Cu, Pb and Ni) throughout the River water, sediments as well as soft tissues of three widely consumed fishes (
Heteropneustes fossilis, Channa punctatus
and
Channa striata
) obtained from two urban streams of the Buriganga and Turag in the Dhaka metropolitan. For evaluating the comparative seasonal variation of heavy-metal concentration, water and sediment samples were collected from five selected sites for two different seasons (viz. 10 from winter seasons and 10 from summer seasons). Finally, a total of 20 water samples, 20 sediment and 12 fish samples were investigated by flame atomic absorption spectroscopy (FAAS) and graphite furnace atomic absorption spectrometer (GFAAS) corrected with the Zeeman effect background correction system. The hierarchy of mean concentration of selected heavy metals in Buriganga water is found to be Fe > Cr > Ni > Zn > Cu > Pb in the winter season whereas during the summer season the order is Fe > Cr > Zn > Ni > Cu > Pb. For the River Turag, the order is Fe > Zn > Cu > Ni > Cr > Pb and Fe > Zn > Ni > Cu > Cr > Pb during winter and summer season, respectively. The level of metals studied surpassed the acceptable level of drinkable water, implying the ineptitude of drinking and cooking water from these Rivers. However, this hierarchy of heavy metals for sediments of Buriganga River changed to Fe > Cr > Ni > Zn > Cu > Pb for the winter season and Fe > Cr > Ni > Cu > Zn > Pb for the summer season. Whereas, for the Turag River, the decreasing trend of metal concentration found in sediment was Fe > Zn > Cr > Ni > Cu > Pb for both seasons. For probable human health hazard implications, contamination factor (CF) and pollution load index (PLI) were studied. The CF values revealed the low-to-moderate pollution of sediment. The PLI value above one shows the degradation of the consistency of the sediments. Fe, Ni, Pb, Cr, Zn and Cu concentrations in fish species were found to be 19.66–45.1, 0.07–12.18, 1.2–10.18, 20.18–187.07, 11.08–68.25, 2.07–10.4 mg/kg, respectively. The metals studied differed considerably among organisms and seasons. Bioconcentration factor (BCF), the daily average consumption of metal (EDI), as well as target threat quotients (THQs) for specific metal indicated that Cr and Pb are harmful in fish muscles and possible risks remain for fish consumers. The obtained concentrations of some metals are higher than the WHO/FAO’s permissible limit, suggesting that the water and fish found in these Rivers are like to be harmful to the human being. This study shows that attention should be given to the risk assessment for heavy metals in these Rivers.
Naturally occurring nanomaterials are finding growing interests in tailoring properties of engineering polymers for advanced applications. The objective of this study was to develop ...environment-friendly nanocomposite films by reinforcing kaolinite nanofillers (1–10 wt%) in silicone rubber (SR) matrix using a simple solvent casting technique. Kaolinite-reinforced films showed substantial improvement in mechanical (tensile strength, Young’s modulus, and elongation at break) and thermal properties at very low filler loading (5 wt%). The improvement of solvent resistance nature of the fabricated films was another critical aspect of this study. Unfilled SR film showed ~19% weight loss when immersed in toluene for 4 h at 25 °C, whereas only ~4% weight loss was recorded in the case of 5% (w/w) kaolinite loaded film. Therefore, kaolinite has the potential to bring significant improvement in the properties of SR. This study indicates that there is plenty of room at the bottom for proper utilization of the potential of kaolinite for developing SR-based composite materials for potential applications in many industries, such as textile, household cleaning, construction, electronics, automotive, medical, etc.
A series of bifunctional nanohybrids containing different proportions of chitosan and titanium dioxide (TiO
2
) were prepared through precipitation technique and applied for removal of a model ...anionic azo dye, Remazol Orange 3R (RO), from aqueous solution. This study reveals the dual benefit of adsorption and photocatalytic degradation of RO by TiO
2
/Chitosan nanohybrids. Nanohybrid fabricated from 80% TiO
2
(w/w) and 20% chitosan (w/w) termed as T
0.80
CS
0.20
removed ∼98.8% RO within only 8 min at pH 2.0 under sunlight irradiation from 60 mg L
−1
dye solution. This was mainly due to the simultaneous role of adsorption and photodegradation activities of nanohybrids. The adsorption performance of T
0.80
CS
0.20
was investigated in terms of the Langmuir isotherm under dark and the maximum adsorption capacity of T
0.80
CS
0.20
for RO was found to be 243.9 mg g
−1
. Electrostatic interaction was suggested as a plausible mechanism for RO adsorption whereas photogenerated holes controlled photocatalytic degradation of RO by producing sufficient quantities of different radical species. In addition, T
0.80
CS
0.20
can be regenerated for removal of RO by simple alkali washing. Therefore, T
0.80
CS
0.20
is recommended as a promising photocatalyst for the removal of RO dye from water.
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