Effect of surface modification on carbon nanotubes (CNTs) catalyzed nitrobenzene reduction by sulfide

Unlocking high-efficiency decontamination by building a novel heterogeneous catalytic reduction system of thiourea dioxide/biochar

Herein, we reported a new contaminant purification paradigm, which enabled highly efficient reductive denitration and dechlorination using a green, stable reducing agent thiourea dioxide (TDO) coupled with biochar (BC) over a wide pH range under anoxic conditions. Specifically, BC acted as both activators and electron shuttles for TDO decomposition to achieve complete anoxic degradation of p-nitrophenol (PNP), p-nitroaniline, 4-chlorophenol and 2,4-dichlorophenol within 2 h. During this process, multiple strongly reducing species (i.e., SO22-, SO2•- and e-/H•) were generated in BC/TDO systems, accounting for 13.3%, 9.7% and 75.5% of PNP removal, respectively. While electron transfer between TDO and H+ or contaminants mediated by BC led to H• generation and contaminant reduction. These processes depended on the electron-accepting capacity and electron-conducting domains of biochar. Significantly, the BC/TDO systems were highly efficient at a pH of 2.0-8.0, especially under acidic conditions, which performed robustly in common natural water constituents.

Palladium doped PDA-coated hercynite as a highly efficient catalyst for mild hydrogenation of nitroareness

Hercynite magnetic nanoparticles were produced through the co-precipitation of ferrous and aluminum cations. The surface of hercynite was respectively coated with silica, 2,4,6-trichloro-1,3,5-triazine, and 1H-pyrazole-3,5-dicarboxylic acid to provide a suitable substrate for Pd(II) loading, furnishing Pd@Her-TCT-PDA. Subsequently, the introduced Pd(II) was reduced to Pd(0) using NaBH4. FT-IR, EDS, XRD, TGA, TEM and SEM images were the characteristic methods to prove the success of catalyst synthesis. The SEM image illustrated the particles with a nanosize of 25-50 nm and TEM image confirmed the presence of Pd nanoparticles with sizes lower than 2 nm. EDS elemental analysis of the catalyst proved the existence of Pd, Fe, and Al atoms along with the C, O, N, and Si atoms belong to the heterocyclic moieties. VSM analysis clarified a considerable drop in the magnetic properties of the hercynite core of the final catalyst due to its modified surface. TGA curve demonstrated that Pd@Her-TCT-PDA contains 20% organic content, attributed to the anchored heterocyclic ligands. Finally, Pd@Her-TCT-PDA was employed along with NaBH4 as a catalytic system to reduce completely the nitro group of aromatic compounds to their corresponding amines. The recyclability tests showed low drop in the catalytic activity of Pd@Her-TCT-PDA after third run with negligible leaching of Pd NPs.

Geobacter sulfurreducens promoted the biosynthesis of reduced graphene oxide and coupled it for nitrobenzene reduction

In order to explore an efficient and green method to deal with nitrobenzene (NB) pollutant, reduced graphene oxide (rGO) as an electron shuttle was applied to enhance the extracellular electron transfer (EET) process of Geobacter sulfurreducens, which was a typical electrochemically active bacteria (EAB). In this study, rGO biosynthesis was achieved via the reduction of graphene oxide (GO) by G. sulfurreducens PCA within 3 days. Also, the rGO-PCA combining system completely reduced 50-200 µmol/L of NB to aniline as end product within one day. SEM characterization revealed that PCA cells were partly wrapped by rGO, and therefore the distance of electron transfer between strain PCA and rGO material was reduced. Beside, the ID/IG of GO, rGO, and rGO-PCA combining system were 0.990, 1.293 and 1.31, respectively. Moreover, highest currents were observed in rGO-PCA-NB as 12.950 µA/-12.560 µA at -408 mV/156 mV, attributing to the faster electron transfer efficiency in EET process. Therefore, the NB reduction was mainly due to: (I) direct EET process from G. sulfurreducens PCA to NB; (II) rGO served as electron shuttle and accelerated electron transfer to NB, which was the main degradation pathway. Overall, the biosynthesis of rGO via GO reduction by Geobacter promoted the NB removal process, which provided a facile strategy to alleviate the problematic nitroaromatic pollution in the environment.

Treasuring industrial sulfur by-products: A review on add-value to reductive sulfide and sulfite for contaminant removal and hydrogen production

Reductive sulfur-containing by-products (S-BPs) released from industrial process mainly exist in the simple form of sulfide and sulfite. In this study, recent advances to remove and make full use of reductive S-BPs to achieve efficient contaminant removal and hydrogen production are critically reviewed. Sulfide, serves as both reductant and nucleophile, can form intermediates with the catalyst surface functional group through chemical interaction, efficiently promoting the catalytic reduction process to remove contaminants. Sulfite assisted catalytic process could be classified to the advanced reduction processes (ARPs) and advanced oxidation processes (AOPs), mainly depending on the presence of dissolved oxygen (DO) in the solution. During ARPs, sulfite could generate reductive active species including hydrated electron (e_aq^-), hydrogen radical (H·), and sulfite radical (SO₃^•-) under the irradiation of UV light, leading to the efficient reduction removal of a variety of contaminants. During AOPs, sulfite could first produce SO₃^•- under the action of the catalyst or energy, initiating a series of reactions to produce oxysulfur radicals. Various contaminants could be effectively removed under the role of these oxidizing active species. Sulfides and sulfites could also be removed along with promoting hydrogen production via photocatalytic and electrocatalytic processes. Besides, the present limitations and the prospects for future practical applications of the process with these S-BPs are proposed. Overall, this review gives a comprehensive summary and aims to provide new insights and thoughts in promoting contaminant removal and hydrogen production through taking full advantage of reductive S-BPs.

Nanoparticle-based toxicity in perishable vegetable crops: Molecular insights, impact on human health and mitigation strategies for sustainable cultivation

With the advancement of nanotechnology, the use of nanoparticles (NPs) and nanomaterials (NMs) in agriculture including perishable vegetable crops cultivation has been increased significantly. NPs/NMs positively affect plant growth and development, seed germination, plant stress management, and postharvest handling of fruits and vegetables. However, these NPs sometimes cause toxicity in plants by oxidative stress and excess reactive oxygen species production that affect cellular biomolecules resulting in imbalanced biological and metabolic processes in plants. Therefore, information about the mechanism underlying interactions of NPs with plants is important for the understanding of various physiological and biochemical responses of plants, evaluating phytotoxicity, and developing mitigation strategies for vegetable crops cultivation. To address this, recent morpho-physiological, biochemical and molecular insights of nanotoxicity in the vegetable crops have been discussed in this review. Further, factors affecting the nanotoxicity in vegetables and mitigation strategies for sustainable cultivation have been reviewed. Moreover, the bioaccumulation and biomagnification of NPs and associated phytotoxicity can cause serious effects on human health which has also been summarized. The review also highlights the use of advanced omics approaches and interdisciplinary tools for understanding the nanotoxicity and their possible use for mitigating phytotoxicity.

Fe-N complex biochar as a superior partner of sodium sulfide for methyl orange decolorization by combination of adsorption and reduction

To enhance the decolorization of methyl orange (MO), Fe-N complex biochar (Fe-N-BC) was developed as an accelerator in the sodium sulfide (Na₂S) reduction system. The decolorization effect and mechanism of MO in the Fe-N-BC/Na₂S composite system were studied. Surface pore analysis, Raman spectroscopy, FT-IR, XPS, and electrochemical analysis were used to characterize Fe-N-BC and unmodified biochar (BC). These results demonstrated that Fe-N-BC had better adsorption performance (specific surface area 463.46 m² g^-1) and electron transfer capacity than BC. By adding Fe-N-BC to the Na₂S reduction system for MO, it was found that the decolorization of MO was greatly improved (increased by 93%). Besides, the effects of critical factors such as the initial concentration of Na₂S, the dosage of Fe-N-BC, pH value, and temperature on the decolorization rate of MO were evaluated. Through the analysis of the action mechanism, the cooperation mode of Fe-N-BC and Na₂S was to form an infinite cycle of adsorption-reduction-regeneration, so as to realize the rapid decolorization of MO. On the one hand, Fe-N-BC could adsorb MO and Na₂S on its surface to increase the contact opportunity; on the other hand, it could act as a redox mediator to accelerate the electron transfer of the reduction reaction. In addition, the degradation of MO by Na₂S was also an in-situ regeneration of Fe-N-BC. These findings may provide a feasible method to decolorize azo dyes quickly by cooperating with chemical reducing agents from a new perspective.

Carbon nanotubes mediated chemical and biological decolorization of azo dye: Understanding the structure-activity relationship

Chemical structure of azo dyes molecules showed significant influence on their decolorization rate, while the structure-activity relationship between chemical structure and their reduction decolorization rate is not fully understand. In this study, we found that azo dye molecule with closer position for electron-withdrawing substituent to azo bond resulted in faster chemical and biotic reduction rate with or without presence of carbon nanotubes (CNTs), while electron-repulsive substituent closer to azo bond leading to slower azo dye chemical and biotic reduction rate no matter with or without presence of CNTs. Additionally, galvanic cell experiments implied that electron transfer process may play important roles for both chemical and biological reduction decolorization of azo dyes, and CV results indicated that the higher (azo bond breakage) reduction wave potential corresponding to a faster azo dye chemical decolorization reaction. Finally, the results of Lowest Unoccupied Molecular Orbital (LUMO) energy established that lower LUMO energy for azo dye corresponding to a faster chemical decolorization reaction. This study not only offer systematized relationships between structure property of azo dye and their decolorization rate, but also provide a universal and propagable reduction rules.

Stimulation of pyrolytic carbon materials as electron shuttles on the anaerobic transformation of recalcitrant organic pollutants: A review

Pyrolytic carbon materials (PCMs) with various surface functionalities are widely used as environmentally friendly and cost-efficient adsorbents for the removal of organic and inorganic pollutants. Recent studies have illustrated that PCMs as electron shuttles (ESs) could also show excellent performances in promoting the anaerobic transformation of recalcitrant organic pollutants (ROPs). Numerous studies have demonstrated the excellent electron-shuttle capability (ESC) of PCMs to stimulate the anaerobic reductive transformation of ROPs. However, there is a lack of consistent understanding of the mechanism of ESC formation in PCMs and the stimulation mechanism for ROPs anaerobic transformation. To gain a more comprehensive understanding of the latest developments in the study of PCMs as ESs for ROPs anaerobic transformation, this review summarizes the formation mechanism, influencing factors, and stimulation mechanisms of ESC. ESC benefits from redox functional groups (quinone and phenol groups), persistent free radicals (PFRs), redox-active metal ions, conductive graphene phase, and porous nature of their surface. The factors influencing ESC include the highest treatment temperature (HTT), feedstocks, modification methods, and environmental conditions, of which, the HTT is the key factor. PCMs promote the reductive transformation of ROPs under anaerobic conditions via abiotic and biotic pathways. Eventually, the prospects for the ROPs anaerobic transformation enhanced by PCMs are proposed.

Abiotic reductive removal of organic contaminants catalyzed by carbon materials: A short review

Since the observation that carbon materials can facilitate electron transfer between reactants, there is growing literature on the abiotic reductive removal of organic contaminants catalyzed by them. Most of the interest in these processes arises from the participation of carbon materials in the natural transformation of contaminants and the possibility of developing new strategies for environmental treatment and remediation. The combinations of various carbon materials and reductants have been investigated for the reduction of nitro-organic compounds, halogenated organics, and azo dyes. The reduction rates of a certain compound in carbon-reductant systems vary with the surface properties of carbon materials, although there are controversial conclusions on the properties governing the catalytic performance. This review scrutinizes the contributions of quinone moieties, electron conductivity, and other carbon properties to the activity of carbon materials. It also discusses the contaminant-dependent reduction pathways, that is, electron transfer through conductive carbon and intermediates formed during the reaction, along with possibly additional activation of contaminant molecules by carbon. Moreover, modification strategies to improve the catalytic activity for reduction are summarized. Future research needs are proposed to advance the understanding of reaction mechanisms and improve the practical utility of carbon material for water treatment. PRACTITIONER POINTS: Reduction rates of contaminants in carbon-reductant systems and modification strategies for carbon materials are summarized. Mechanisms for the catalytic activity of carbon materials are discussed. Research needs for new insights into carbon-catalyzed reduction are proposed.

Cytotoxicity of functionalized CeO2 nanoparticles towards Escherichia coli and adaptive response of membrane properties

The cytotoxicity and mechanisms of cerium oxide nanoparticles (CeO₂-NPs) on organisms have attracted great concerns recently, while that of CeO₂-NPs with functional groups remains unclear. This study investigated cytotoxic effects and mechanisms of CeO₂-NPs with hydroxyl, carboxyl, or amino functional groups towards a strain Escherichia coli (E. Coli). Results showed that CeO₂-NPs produced a stronger cytotoxicity in NaCl medium than in PBS medium at the concentrations of 10-400 mg/L. The toxicity followed the order of CeO₂-COOH > CeO₂-NH₂ > CeO₂-OH. Exposing to CeO₂-NPs increased cell membrane permeability and reduced membrane fluidity. The membrane phospholipid fatty acid compositions also varied greatly as a response to the stress of CeO₂-NPs, with the proportion of unsaturated fatty acids increased and saturated fatty acids decreased. Both intracellular reactive oxygen species (ROS) level and malonaldehyde (MDA) level declined, suggesting the oxidative stress from ROS may be not the primary reason for the membrane damage. Other mechanisms such as direct membrane oxidation by Ce⁴⁺ or physical penetration based on a close contact between nanoparticles and microbes might contribute to the membrane damages and cell viability loss. The present study provides a significant insight into the influence of functionalized CeO₂-NPs on a gram-negative bacterium.

A self-boosting microwave plasma strategy tuned by air pressure for the highly efficient and controllable surface modification of carbon

Surface modification is required to improve the activity and compositing ability of carbonaceous materials for their application in numerous areas such as energy storage, aerospace applications, and construction reinforcement. However, current strategies are facing problems such as the involvement of expensive and corrosive chemicals, poor controllability, and breakage of the carbon skeleton, thus sacrificing the mechanical and electrical properties. In this study, a green and controllable self-boosting microwave technology is proposed for the high-efficient surface modification of carbon. Air was used as the only oxidant. A carbon fiber cloth (CFC) is exposed to microwave irradiation in air for 90 s, yielding CFC with a surface oxygen content of 25.73%, 54.41%, and 52.56% at 1 atm, 8000 Pa, and 80 Pa, respectively, as determined via X-ray photoelectron spectroscopy. Notably, the content of each oxygen-containing functional group (e.g., -C-OH and -C[double bond, length as m-dash]O) is controllable by tuning the air pressure. Besides, CFC has enhanced mechanical and electrical properties. In comparison, CFC treated with a strong acid for 2 h only has a surface oxygen content of 21.4%, exhibiting greatly impaired electrical and mechanical properties. Numerical simulations at different pressures suggest that air plasma is triggered and boosted by the existence of CFC at 8000 Pa and 80 Pa, generating different electron number densities and electron temperature distributions, thus resulting in high-efficient and controllable modification.

Sulfide-induced reduction of nitrobenzene mediated by different size fractions of rice straw-derived black carbon: A key role played by reactive polysulfide species

Here we investigated the mediation efficiency of different size fractions of rice straw-derived black carbon (BC) using sulfide-induced nitrobenzene reduction as a model system. The bulk BC was divided into three size fractions: dissolved BC (size <0.45 μm), colloidal BC (0.45 μm < size < 1 μm), and particulate BC (size > 1 μm). With the presence of BC fractions (250 mg/L) nitrobenzene reduction by Na₂S was significantly facilitated, wherein the mediation efficiency was positively correlated with the BC fraction's oxygen group content in an order of particulate BC < colloidal BC ≪ dissolved BC. Consistently, the oxidation treatment of particulate BC with O₃ or HNO₃ improved the mediation efficiency, whereas the reduction treatment with NaBH₄ reduced the mediation efficiency. The supernatant collected with dialysis or filtration of suspension of BC materials pre-reacted with Na₂S could effectively reduce nitrobenzene, suggesting that reactive reducing sulfur species were produced in aqueous solutions by reacting sulfide only with BC materials. This was evidenced by the fact that polysulfides and polysulfide radicals were both detected in the supernatant. As demonstrated by electron paramagnetic resonance analysis, the quinone moieties at the surface of BC materials accepted electrons from sulfide and turned into semiquinone free radicals, consequently leading to formation of reactive reducing sulfur species and thus enhanced nitrobenzene reduction. The strong mediation efficiency on redox reactions observed for colloidal BC and dissolved BC combined with their significant mobility in subsurface environments indicate that these carbonaceous materials may play an important role in the fate process of organic contaminants as both carriers and catalysts. CAPSULE: The surface quinone moieties of BC induce the formation of reactive reducing sulfur species by acting as one-electron acceptors and facilitate nitrobenzene reduction by sulfide.

Effective stabilization and distribution of emulsified nanoscale zero-valent iron by xanthan for enhanced nitrobenzene removal

The reactivity and delivery of remediants and treatment of organic contaminants in heterogeneous aquifer are particularly challenging issues for injection-based remedial treatments. Our objective was to enhance the reactivity and delivery of nanoscale zero-valent iron (nZVI) and improve the sweeping efficiency of nZVI into low permeable zones (LPZs) to reduce nitrobenzene (NB). This was accomplished by conducting batch and transport experiments that quantified NB degradation by different modified nZVI and the ability of emulsified nZVI (EZVI) or xanthan carried EZVI (XG-EZVI) to penetrate and cover a lens. By incorporating the xanthan and emulsified oil with nZVI, it possessed higher stability and stronger reactivity to reduce NB. Results showed that the stability of EZVI was improved by xanthan, and there were no adverse effects on NB removal in use of XG-EZVI at limited xanthan addition of ≦100 mg L^-1. By the injection of XG-EZVI in 2D-tank experiments, the degradation of NB was 8 times that of EZVI added, while NB adsorption on media was only 1/50 of initial NB. 1205 mg of NB totally entered into the tank, the quality of aniline in effluent was approximately 90.0 mg in addition of XG-EZVI at 40 h, but not detected in presence of EZVI. The greater NB reduction by XG-EZVI resulted from higher sweeping efficiency in LPZ. These observations support the couple use of xanthan and emulsified oil for modifying nZVI as a means of achieving greater stability and reactivity and enhancing nZVI delivery into LPZs for the treatment of NB.

Undiscovered Mechanism for Pyrogenic Carbonaceous Matter-Mediated Abiotic Transformation of Azo Dyes by Sulfide

Pyrogenic carbonaceous matter (PCM) catalyzes the transformation of a range of organic pollutants by sulfide in water; however, the mediation mechanisms are not fully understood. In this study, we observed for the first time that the degradation of azo dyes by sulfide initially underwent a lag phase followed by a fast degradation phase. Interestingly, the presence of PCM only reduced the lag phase length of the azo dye decolorization but did not significantly enhance the reaction rate in the fast degradation phase. An analysis of the azo dye reduction and polysulfide formation indicated that PCM facilitated the transformation of sulfide into polysulfides, including disulfide and trisulfide, resulting in fast azo dye reduction. Moreover, the oxygen functional groups of the PCM, especially the quinones, may play an important role in the transformation of sulfide into polysulfides by accelerating the electron transfer. The results of this study provide a better understanding of the PCM-mediated abiotic transformation of organic pollutants by sulfide in anaerobic aqueous environments.

Computer-Aided Exergy Sensibility Analysis of Nitrobenzene Production through Benzene Nitration Using an Acid Mixture

Nitrobenzene is widely produced via benzene nitration to be applied in several industries such as pharmaceutical, textile, and agricultural. In this work, an exergy sensibility analysis was performed with the aim of identifying possible opportunities of process improvements. The irreversibilities, exergy of wastes, and efficiency were calculated per stage through exergy balance. The simulation software Aspen plus V10.1 provided the physical exergies of process streams while chemical exergies were found in literature. A sensibility analysis was also carried out in order to study the effect of efficiency of some stages (polyfunctional reaction and cooling 1) on global exergy efficiency. This analysis reveals that nitrobenzene production from benzene is an efficient process from an exergy viewpoint (88%). The total irreversibilities, total exergy of wastes, and exergy of utilities-inlet were calculated in 41,647,341.85 MJ/h, 5,537,487.3 MJ/h, and 18,137,363.71 MJ/h, respectively. The results obtained from sensibility analysis suggested that heat flow of heat exchangers HE-201, HE-303, and HE-301 could provide energy requirements for heating.

Shear-Thickening Fluid Using Oxygen-Plasma-Modified Multi-Walled Carbon Nanotubes to Improve the Quasi-Static Stab Resistance of Kevlar Fabrics

The excellent mechanical property and light weight of protective materials are vital for practical application in body armor. In this study, O₂-plasma-modified multi-walled carbon nanotubes (M-MWNTs) were introduced into shear-thickening fluid (STF)-impregnated Kevlar woven fabrics to increase the quasi-static stab resistance and decrease the composite weight. The rheological test showed that the addition of 0.06 wt. % M-MWNT caused a marked increase in the peak viscosity from 1563 to 3417 pa·s and a decrease in the critical shear rate from 14.68 s-1 to 2.53 s-1. The storage modulus (G') and loss modulus (G″) showed a higher degree of abrupt increase with the increase of shear stress. The yarn pull-out test showed that the yarn friction of M-MWNT/STF/Kevlar fabrics was far superior to the original fabrics. Importantly, under similar areal density, the M-MWNT/STF/Kevlar fabrics could resist 1261.4 N quasi-static stab force and absorb 41.3 J energy, which were much higher than neat Kevlar fabrics. The results of this research indicated that quasi-static stab resistance was improved by M-MWNTs, which was attributed to the excellent shear-thickening effect and the high yarn friction. Therefore, M-MWNT/STF/Kevlar fabrics have a broad prospect in the fields of body protection.