One-pot green synthesis of silver/iron oxide composite nanoparticles for 4-nitrophenol reduction

Pd@Na-CMC/g-C3N4: A nanostructured catalyst system based on sodium carboxymethyl cellulose/graphitic carbon nitride hydrogel beads and its performance in the treatment of organic and inorganic pollutants in water

The chemical reduction of organic or inorganic water contaminants is very important for both human health and pollution control. However, challenges still persist in preparing catalysts for chemical reduction, and there is a need for the development of inexpensive, easily synthesized, and effective catalyst systems. In this study, we have synthesized a new palladium nanocatalyst supported on the composite hydrogel beads composed of sodium carboxymethyl cellulose (Na-CMC) and graphitic carbon nitride (g-C3N4). The Pd@Na-CMC/g-C3N4 composite was fully characterized using FE-SEM, XRD, BET, EDS, TEM, and EDS mapping analysis, confirming its successful preparation at the nano-scale. Pd@Na-CMC/g-C3N4 was utilized to reduce various nitroaromatics such as 4-nitrophenol (4-NP), 2-nitrophenol (2-NA), 4-nitroaniline (4-NA), 4-nitro-o-phenylenediamine (4-NPDA), and organic dyes including methylene blue (MB), methyl orange (MO), Rhodamine B (RhB), as well as potassium hexacyanoferrate(III) (K3[Fe(CN)6]), which is the inorganic contaminant. While Pd@Na-CMC/g-C3N4 completely reduced nitroaromatics within 65-120 s at 1 × 10-4 M concentration, organic dyes within 0-60 s at 1 × 10-5 M concentration, and K3[Fe(CN)6] within 90 s at 0.002 M concentration in water at room temperature. Rate constant values (kapp) of 4-NP, 2-NA, 4-NA, 4-NPDA, MO, RhB, and K3[Fe(CN)6] were calculated to be 0.0085 s-1, 0.012 s-1, 0.016 s-1, 0.01 s-1, 0.013 s-1, 0.021 s-1, and 0.015 s-1, respectively. Additionally, the Pd@Na-CMC/g-C3N4 displayed high stability and even after four consecutive runs, it was able to reduce 4-NP and MO without any significant loss in its performance.

Green synthesis of magnetic silver nanocomposite: the photocatalytic performance of nanocomposite to decolorize organic dyes

The magnetite-silver nanocomposites (Fe3O4-Ag NCs) were synthesized via a facile and green process by Citrus sinensis peel extract. The deposition of silver nanoparticles (NPs) was confirmed by observing an absorption peak at the maximum wavelength at 422 nm in the suspension solution of samples, which is related to silver surface plasmon resonance (SPR). The characteristic diffraction patterns of Fe3O4 and Ag phases were characterized utilizing the XRD patterns and the average size of the crystals was 21 nm. The photocatalytic behavior of Fe3O4-Ag NCs was studied for the destruction of three organic dyes methyl green (MG), methyl orange (MO), and methylene blue (MB) below UV radiation. The effect of the amount of photocatalyst and volume of hydrogen peroxide as an oxidant in the process of dye degradation was also investigated. The complete degradation time of dyes MB, MG, and MO under UV irradiation in the presence of 0.002 g Fe3O4-Ag NCs were 57, 33, and 49 min, respectively. The time of degradation reactions showed the high photocatalytic performance of Fe3O4-Ag NCs. These results proved that the synergistic effect of magnetite in the role of supporting the silver NPs was a significant contribution to the excellent decolorization behavior of Fe3O4-Ag NCs.

Multifunctional Ti3C2Tx MXene/Silver Nanowire Membranes with Excellent Catalytic, Antifouling, and Antibacterial Properties for Nitrophenol-Containing Water Purification

The uncontrolled release of nitrophenol and dye pollutants into water systems is an increasingly serious worldwide concern, and thus efficient wastewater treatment technologies are urgently needed. Herein we report a novel two-dimensional (2D) transition metal carbides and/or nitrides (Ti3C2Tx MXene) membrane modified with silver nanowires (AgNWs) by vacuum assisted filtration technology for the ultrafast nitrophenol catalysis and water purification applications. Regular and controllable membrane transport channels were constructed by stacking Ti3C2Tx MXene nanosheets. Furthermore, the intercalation of AgNWs into the Ti3C2Tx MXene interlayer greatly enlarged the interlayer spacing, resulting in more gaps for fast and selective molecular transport. The optimized Ti3C2Tx MXene@AgNWs (M@A) membrane exhibited a water flux up to ∼191.9 L/(m2 h) while maintaining a high bovine serum albumin (BSA) rejection of ∼95.4%. We emphatically used M@A membranes as efficient catalysts for the reduction of 4-nitrophenol (4-NP), and the results indicated that M@A-12% membrane exhibited the greatest catalytic reduction ability, and recycling utilization. M@A-12% membrane also had an antibacterial rate of more than 99% against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). This work provides a possibility to expand the application of 2D multifunctional M@A membranes in wastewater treatment and pollutant catalytic degradation.

The Green Synthesis of Silver Nanoparticles from Avena fatua Extract: Antifungal Activity against Fusarium oxysporum f.sp. lycopersici

Using plant extracts as eco-friendly reducing and stabilizing agents for the synthesis of nanoparticles has gained significant attention in recent years. The current study explores the green synthesis of silver nanoparticles (AgNPs) using the Avena fatua extract and evaluates their antifungal activity against Fusarium oxysporum f.sp. lycopersici (Fol), a fungal plant pathogen. A green and sustainable approach was adopted to synthesize silver nanoparticles before these nanoparticles were employed for anti-fungal activity. The primary indication that AgNPs had formed was performed using UV-vis spectroscopy, where a strong peak at 425 nm indicated the effective formation of these nanoparticles. The indication of important functional groups acting as reducing and stabilizing agents was conducted using the FTIR study. Additionally, morphological studies were executed via SEM and AFM, which assisted with more effectively analyzing AgNPs. Crystalline behavior and size were estimated using powder XRD, and it was found that AgNPs were highly crystalline, and their size ranged from 5 to 25 nm. Synthesized AgNPs exhibited significant antifungal activity against Fol at a concentration of 40 ppm. Furthermore, the inhibitory index confirmed a positive correlation between increasing AgNPs concentration and exposure duration. This study suggests that the combined phytochemical mycotoxic effect of the plant extract and the smaller size of synthesized AgNPs were responsible for the highest penetrating power to inhibit Fol growth. Moreover, this study highlights the potential of using plant extracts as reducing and capping agents for the green synthesis of AgNPs with antifungal properties. The study concludes that A. fatua extract can synthesize antifungal AgNPs as a sustainable approach with robust antifungal efficacy against Fol, underscoring their promising potential for integration into plant protection strategies.

Structural and optical properties of silver supported α-Fe2O3 nanocomposite fabricated by Saraca asoca leaf extract for the effective photo-degradation of cationic dye Azure B

In recent decades, several nanocomposites developed by chemical synthetic routes, have been demonstrated as efficient photocatalysts for the photodegradation of hazardous organic dyes. The present investigation reports the sonochemical-assisted fabrication of silver-supported α-Fe2O3 nanocomposites (SA@Ag@IONCs) using the Saraca asoca leaf extract. The magnetic nanocomposites can be easily removed from the reaction mixture. The morphology of these materials was characterized by field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), XPS, BET surface area analyzer, UV-visible spectroscopy, photoluminescence, X-ray diffraction (XRD), and VSM techniques. The XRD and electron microscopy analyses revealed the small size and well-crystalline SA@Ag@IONC particles with spherical and buckyball structures. The large surface area of SA@Ag@IONCs was confirmed by BET analysis. The absorption edge in UV-visible spectra appeared to migrate towards high wavelengths for the SA@Ag@IONC composite, causing a change in the bandgap energy. In the case of the sonication assisted composite, the bandgap energy was 2.1 eV, making it easier for the electron to transfer from the valence band to conduction band. The decoration of ultrasmall silver onto the surfaces of the α-Fe2O3 nanocomposite, which considerably increases the capacity to absorb sunlight, enhances the efficiency of charge carrier separation, and inhibits the electron-hole recombination rate as confirmed by the reduced PL intensity, is responsible for the excellent photocatalytic degradation performance. Outcomes shown SA@Ag@IONCs have a high photodegradation rate as well as high-rate constant value at an optimized condition that is at pH 9 and 0.5 g L-1 dose of nanocomposite, photodegradation rate of Azure B is ∼94%. Trap experiment results indicated that O2˙- and h+ are the active species responsible for the photodegradation of AzB.

Aboyewa J, Moabelo KL, Sibuyi NRS, Meyer S, Onani MO, Meyer M, Madiehe AM. Anticancer, Antioxidant, and Catalytic Activities of Green Synthesized Gold Nanoparticles Using Avocado Seed Aqueous Extract

Disposal of agricultural waste has a negative impact on the environment and human health and may contribute to the greenhouse effect. The field of nanotechnology could provide alternative solutions to upcycle agricultural wastes in a safer manner into high-end value products. Organic waste from plants contain biomaterials that could serve as reducing and capping agents in the synthesis of nanomaterials with enhanced activities for use in biomedical and environmental applications. Persea americana (avocado) is a fruit with a high nutritional value; however, despite its rich phytochemical profile, its seed is often discarded as waste. Therefore, this study aimed to upcycle avocado seeds through the synthesis of gold nanoparticles (AuNPs) and evaluate their anticancer, antioxidant, and catalytic activities. The biosynthesis of avocado seed extract (AvoSE)-mediated AuNPs (AvoSE-AuNPs) was achieved following the optimization of various reaction parameters, including pH, temperature, extract, and gold salt concentrations. The AvoSE-AuNPs were poly-dispersed and anisotropic, with average core and hydrodynamic sizes of 14 ± 3.7 and 101.39 ± 1.4 nm, respectively. The AvoSE-AuNPs showed excellent antioxidant potential in terms of ferric reducing antioxidant power (343.88 ± 0.001 μmolAAE/L), 2,2-diphenyl-1-picrylhydrazyl (128.80 ± 0.0159 μmolTE/L), and oxygen radical absorbance capacity (1822.02 ± 12.6338 μmolTE/L); significantly reduced the viability of Caco-2 and PC-3 cells in a dose-dependent manner; and efficiently reduced 4-nitrophenol (4-NP) to 4-aminophenol. This study demonstrated how avocado seeds, an agricultural waste, can be used as sources of new bioactive materials for the synthesis of AuNPs, which have excellent antioxidant, anticancer, and catalytic activities, showing AvoSE-AuNPs' versatility in various applications. In addition, the AvoSE-AuNPs exhibited good stability and recyclability during the catalytic activity, which is significant because some of the primary issues with the use of metallic NPs as catalysts are around the cost-effectiveness, recovery, and reusability of the catalyst.

Type-II ternary Bi2WO6/rGO/SnFe2O4 heterojunction nanocomposites and their photocatalytic efficiency towards 4-nitrophenol reduction

In this study, tin ferrite (SnFe₂O₄-spinel) and bismuth tungstate (Bi₂WO₆) encapsulated on reduced graphene oxide (rGO) were synthesised using the hydrothermal method. This heterostructure nanocomposite was characterised using Fourier transform infrared spectroscopy (FT-IR), Ultraviolet-visible spectroscopy (UV-Vis), powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), FT-Raman Spectroscopy (FT-Raman) and X-ray photoelectron spectroscopy (XPS) methods. The powder XRD results showed an increase in lattice parameters and a decrease in size when SnFe₂O₄ and Bi₂WO₆ were encapsulated on rGO. The catalytic activity of the type-II ternary Bi₂WO₆/rGO/SnFe₂O₄ heterojunction nanocomposite was checked using a model reduction reaction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of NaBH₄ as the reducing agent under light exposure. Bi₂WO₆/rGO/SnFe₂O₄ showed better catalytic efficiency than the individual components like SnFe₂O₄, rGO/SnFe₂O₄, Bi₂WO₆, rGO/Bi₂WO₆ and Bi₂WO₆/SnFe₂O₄ nanocomposites. Thus, the type-II ternary Bi₂WO₆/rGO/SnFe₂O₄ heterojunction nanocatalyst with better surface area and lower surface energy could be considered as a promising UV-light sensitive catalyst for the detoxification of various environmental pollutants and for other environmental remediations.

Ag2O-adorned ZnO nanostructures: cooperative and sustainable nanomaterial system for effective reduction and mineralization of hazardous water pollutants

Organic water pollutants like nitroaromatics and synthetic dyes are causing serious threats to water. Ever-growing urban and industrial activities along with population explosion are rapidly contributing severe level of water contamination. Semiconducting nanomaterial-based photocatalysis has been proven to be an effective process for degradation of organic water pollutants. In the current study, visible light active Ag₂O-adorned ZnO nanostructures were fabricated by a simple two-step hydrothermal method and the prepared nanostructures were utilized for the photocatalytic mineralization of rhodamine B (RhB) dye with visible light radiation. The catalytic potential of as-synthesized nanostructures was also investigated for the reduction of nitroaromatics (4-NP and 4-NA) and RhB dye in the presence of NaBH₄. The Ag₂O-adorned ZnO nanostructures prepared with 5% of silver nitrate denoted as ZnO/Ag₂O (5%) demonstrated stupendous photomineralization activity against RhB dye as almost 100% degradation of RhB dye was achieved within 100 min of reaction time at pH = 6. The kinetic study revealed that the degradation reaction followed the pseudo-first-order kinetics and the kinetic rate constant (k) of photodecolorization reaction for optimal catalyst was calculated to be 61.4 × 10^-3 min^-1. The nanostructures revealed excellent recyclability and photostability as 95% activity of the catalyst was preserved even after the fifth cyclic run. The catalytic reduction of the 4-NP, 4-NA, and RhB dye was completed in 21, 12, and 40 min, respectively, in the presence of ZnO/Ag₂O (5%) and NaBH₄ solution. The kinetic rate constant values for the reduction reactions were determined to be 229.6 × 10^-3, 454.2 × 10^-3, and 105.5 × 10^-3 min^-1 for 4-NP, 4-NA, and RhB dye, respectively. Thus, the obtained results suggest that the components of the prepared nanosystem help in mutually strengthening the catalytic and photocatalytic abilities of each other, indicating the development of a cooperative and sustainable nanomaterial system in the current study.

Catalytic performance of PVP-coated CuO nanosheets under environmentally friendly conditions

Aromatic nitro compounds are an increasing concern worldwide due to their potential toxicity, prompting a quest for efficient removal approaches. This study established a simple and environmentally friendly method to synthesize a highly efficient, recoverable and stable CuO nanosheets catalyst to overcome public health and environmental problems caused by nitro aromatic compounds. In the current research, the effect of different concentrations of copper nitrate on the size and shape of CuO nanostructures in the chemical synthesis was studied. The CuO nanosheets were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectrophotometry. It was found that at concentrations of 0.07 M and 0.1 M of copper nitrate, pure CuO was formed. The FTIR results showed that carbonyl group in PVP coordinated with CuO and formed a protective layer. The as-synthesized CuO nanosheets with an average width of 60 ± 23 nm and length of 579 ± 154 were used as a catalyst for highly selective and efficient reduction of aromatic nitro and aromatic carboxylic acid to the corresponding amine and alcohol compounds. The reduction reaction was monitored by either UV-Vis absorption spectroscopy or high performance liquid chromatography (HPLC). 4-Nitrophenol and 4-nitroaniline were reduced to corresponding amine compounds within 12 min and 6 min, respectively in the presence of a reasonable amount of catalyst and reducing agent. The CuO nanosheets also exhibited excellent stability. The catalyst can be reused without loss of its activity after ten runs.

N-substituted CQDs impregnated by Fe3O4 heterostructure: Bifunctional catalyst for electro-catalytic and photo-catalytic detection of an environmental hazardous organic pollutant

ortho-Nitroaniline (o-NA) compounds are deemed to be a strongly toxic pollutant in nature and potentially carcinogenic; however, they are frequently utilized to synthesize dyes, pesticides, medicines, fungicides, pigments, and other organic chemicals. Their detection in an aqueous medium is fundamentally required to avoid the potential hazardous being created by these compounds. In this study, a novel sensor based on an Iron oxide (Fe3O4) containing highly dispersed nitrogen-doped carbon quantum dots (N-CQDs@Fe3O4 NFs) was demonstrated for the electrochemical detection of o-NA using differential pulse voltammetry (DPV) and cyclic voltammetry (CV) techniques. N-CQDs@Fe3O4 NFs were synthesized by hydrothermal method and studied by various analytical and spectroscopy techniques, which collectively reveal that the as-prepared composite has superior physical and chemical properties. The DPV study indicated that the o-NA sensor had a good limit of detection, linear range, and sensitivity in the range of 1.2 nm, 0.03-386.84 μM, and 36.5575 μA μM-1 cm-2, respectively, along with the sensor showed superior sensitivity when compared to the previously reported modified electrodes. Further, N-CQD/Fe3O4 NFs worked as heterogeneous catalysts for the photocatalytic reduction of o-NA to o-phenylenediamine (o-PD) in an aqueous medium. The reaction was examined under UV-Visible spectroscopy, and the complete photocatalytic reduction was observed for the N-CQD/Fe3O4 NFs in about 6 min with 96% as compared to other control samples; thus, authenticating the superiority of the synthesized composite in rendering the real-time applications.

Cationic Polystyrene Resin Bound Silver Nanocomposites Assisted Fourier Transform Infrared Spectroscopy for Enhanced Catalytic Reduction of 4-Nitrophenol in Aqueous Medium

The present work reported a novel strategy to construct supported cationic-polystyrene-resin-bound silver nanocomposites for enhanced catalytic reduction of 4-nitrophenol in an aqueous medium. The Fourier transform infrared spectroscopy (FTIR) was used as a model instrument for the study of catalytic reduction of 4-nitrophenol using cationic-polystyrene-resin-bound silver nanocomposite materials. The mechanism is based on the reduction of 4-nitrophenol to 4-aminophenol due to the electron transfer process that occurred between donor borohydride (BH4−) and acceptor 4-nitrophenol. The polystyrene resin provides support and surface area to increase the catalytic activity of silver nanoparticles. The diffused reflectance-Fourier transform infrared spectroscopy revealed the binding of silver particles onto the surface of cationic polystyrene resin beads. Furthermore, the catalyst was easily separated by the filtration and drying process and was able to reuse. A quantitative analysis of this work has also been performed. The linearity range, the limit of detection, and the limit of quantification obtained for the present method were 0.1 × 10−4 to 1.0 M, 0.6 M, and 2.1 M, respectively. Moreover, a good catalytic efficiency was found to be 96.8%. The advantages of the current method are its simplicity, sensitivity, rapidity, low cost, ease of preparation, and excellent catalytic efficiency to reduce 4-nitrophenol from an aqueous solution.

Synthesis of a Ag/rGO nanocomposite using Bos taurus indicus urine for nitroarene reduction and biological activity

The present study develops a unique in situ synthesis of a catalytically and biologically active Ag/reduced graphene oxide (rGO) nanocomposite. Herein, we employed Bos taurus indicus urine to synthesize a Ag/rGO nanocomposite in an environmentally benign, facile, economical, and sustainable manner. The elemental composition analysis reveals the presence of Ag, O and C elements. The scanning electron micrograph shows the formation of spherical silver in nanoform whereas rGO is found to be flake shaped with a wrinkled nature. The synthesized nanomaterial and its composite shows a positive catalytic effect in simple organic transformation for the reduction of nitroarene compounds. Investigations were conducted into the catalytic effectiveness of the prepared nanomaterials for diverse nitroarene reduction. Then, using NaBH₄ at 25 °C, the catalytic roles of Ag and the Ag/rGO nano-catalyst were assessed towards the catalytic reduction of several environmental pollutants such as 2-, 3- and 4-nitroaniline and 4-nitrophenol into their respective amino compounds. To test their catalytic performance, bio-mimetically synthesized Ag NPs were thermally treated at 200 °C and compared with the Ag/rGO nanocomposite. Furthermore, biomedical applications such as the antibacterial and antioxidant properties of the as-prepared nanomaterials were investigated in this study.

TiO2 ceramic membrane decorated with Fe3O4-Ag composite nanoparticles for produced water treatment

This study focused on the surface modification of commercial TiO₂ membranes with Fe₃O₄ decorated silver (Ag) nanoparticles (Fe₃O₄-Ag) via chemical attachment. Firstly, the Ag concentration on Fe₃O₄ was optimized, and different composites were prepared and characterized. Secondly, the optimal composite was used to prepare novel TiO₂/Fe₃O₄-Ag ceramic membranes via surface coating through tetraethyl orthosilicate (TEOS) crosslinking. The membranes were characterized using SEM, EDX, FTIR, XRD, and contact angle. Biofouling resistance of the membranes was investigated using the Coomassie Blue dye method. The coated membranes were tested for water flux, chemical oxygen demand (COD) rejection, and biofouling resistance. Results showed that all coated membranes exhibited higher water flux. For example, the membrane with a 1.25 wt% Fe₃O₄-Ag coating showed the highest filtration flux of 1445 L/m²h (LMH) compared to the pristine membrane (379 LMH) without compromising the COD rejection. The resistance of the membrane to biofouling increased with the increase of Fe₃O₄-Ag nanoparticle concentration. The obtained results demonstrate the great potential of TiO₂/Fe₃O₄-Ag ceramic membranes for the treatment of produced water.

Comprehensive Study on Lemon Juice-Based Green Synthesis and Catalytic Activity of Bismuth Nanoparticles

Bismuth nanoparticles have gained considerable interest in catalysis because of their small size, large surface-to-volume ratio, and low toxicity. In spite of these advantages, the toxic reagents and solvents used in the synthetic process are significant limitations to their development and utilization. In this study, a green approach employing easily accessible lemon juice was applied for the synthesis of bismuth nanoparticles (BiNPs) as a green alternative to conventional chemical ones. This study clarified the formation and growing process of green-synthesized BiNPs using lemon juice as a reducing and capping agent. The reaction time and amounts of lemon juice significantly affect the growth, morphology, and stability of BiNPs, as confirmed from XRD, DLS, SEM, and TEM analyses. The synthesized BiNPs effectively catalyzed the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH₄, and the reduction was significantly accelerated by sunlight and the removal of the fibrous coating layer around BiNPs. Moreover, the synthesized BiNPs also show excellent catalytic efficacy toward the reduction of organic dyes, namely, methyl orange, methylene blue, and rhodamine B. All catalytic reductions followed the pseudo-first-order kinetics, and the rate constants are in the order of k _MB > k _RhB > k _MO > k _4-NP. The stated biogenic synthetic route paves the way for the green industrial fabrication of BiNPs and their uses in catalysis for wastewater treatment.

Ferric Chloride-Induced Synthesis of Silver Nanodisks with Considerable Activity for the Reduction of 4-Nitrophenol

Silver nanodisks (AgNDs) have been successfully synthesized by using ferric chloride as an auxiliary agent in the presence of polyvinylpyrrolidone and N,N-dimethylformamide as both a solvent and a reducing agent. The mass ratio of reactants, temperature, and time were demonstrated to be the key factors determining the morphology of the product, and the conversion of Fe³⁺/Fe²⁺ ions played an important role in increasing the ratio of silver nanosheets (AgNSs). As the reaction prolonged, the etching effect of Cl^- ions on the tips of AgNSs became more and more obvious, which made the obtained typical polygonal AgNSs turn into AgNDs eventually. In addition, the prepared AgNDs exhibited a considerable catalytic activity in the reduction of 4-nitrophenol.

Different Fuel-Adopted Combustion Syntheses of Nano-Structured NiCrFeO4: A Highly Recyclable and Versatile Catalyst for Reduction of Nitroarenes at Room Temperature and Photocatalytic Degradation of Various Organic Dyes in Unitary and Ternary Solutions

As industrialization progresses, there is a large release of hazardous pollutants into the environment. These pollutants, which contain nitro compounds and organic dyes, are extremely dangerous due to their toxic and carcinogenic nature. An efficient, environmentally benign, and economical catalyst to degrade environmental pollutants or convert them into useful products has been of sustained interest in recent years. In this context, we report a simple and inexpensive combustion fabrication of NiCrFeO₄ using different fuels such as glycine, polyvinyl alcohol (PVA), and urea, showing tremendous catalytic and photocatalytic functionalities. Rietveld refinement and X-ray diffraction studies confirmed the formation of single-phase ferrites, with crystallite sizes ranging from 3.9 to 43.31 nm. The values of optical band gap, obtained from the diffused reflectance spectroscopy technique, lie in the visible region range (1.50-1.60 eV), and hence, all the synthesized ferrites can act as good photocatalysts in the presence of visible light. All the NCF nanocatalysts were utilized for the reduction of nitroarenes and photocatalytic degradation of various cationic (RhB and MB) and anionic (MO) dyes and their mixture. NCFP displayed excellent activity for the reduction and oxidation reactions owing to its large surface area and low optical band gap. Furthermore, the photo-oxidative degradation by NCFP was also enhanced due to its low recombination of charge carriers as confirmed by the photoluminescence (PL) spectroscopy. NCFP efficiently reduces nitrobenzene to aminobenzene with 95% yield using sodium borohydride as the reducing agent in methanol medium at RT in 10 min. The results of photocatalytic activity have shown that the degradation efficiency of NCFP follows the order RhB > MB > MO in their unitary solution. Furthermore, in the case of the mixture of dyes, NCFP showed enhanced photocatalytic degradation for cationic dyes (RhB and MB) compared to that of anionic dye (MO). From the performance point of view, this catalyst can be useful in industrial application because of its high stability, greater catalytic efficiency, and cost-effectiveness.

Biogenic synthesis of silver anchored ZnO nanorods as nano catalyst for organic transformation reactions and dye degradation

In this study, we are reporting biogenic synthesis of silver nanoparticles and hydrothermal synthesis of zinc oxide nanoparticles. Using convenient mechanical milling methods, nanocomposites with superior photocatalytic and catalytic properties are synthesized. Herein, we have adopted a green, eco-friendly, and economical route for the synthesis of Ag nanoparticles using Zingiber officinalae rhizome extract in an aqueous solution. The synthesized materials were characterized using UV–Vis spectroscopy, XRD, SEM & FE-SEM, FT-IR, Raman, and a particle size analyzer with zeta potential analysis. The photocatalytic activities of Ag, ZnO and their composites were studied by observing the degradation of methylene blue and crystal violet dyes under natural sunlight. Then the catalytic efficacies of synthesized nanoparticles for various organic transformation reactions were studied. Ag–ZnO nanocomposites were predicted to have improved photocatalytic activity and organic transformation reactions, allowing them to be used in environmental remediation applications.

Template free-synthesis of cobalt-iron chalcogenides [Co0.8Fe0.2L2, L = S, Se] and their robust bifunctional electrocatalysis for the water splitting reaction and Cr(vi) reduction

The ease of production of materials and showing multiple applications are appealing in this modern era of advanced technology. This paper reports the synthesis of a pair of novel cobalt–iron chalcogenides [Co_0.8Fe_0.2S₂ and Co_0.8Fe_0.2Se₂] with enhanced electro catalytic activities. These ternary metal chalcogenides were synthesized by a one-step template-free approach via a hexamethyldisilazane (HMDS)-assisted synthetic method. Transient photocurrent (TPC) studies and electrochemical impedance spectra (EIS) of these materials showed free electron mobility. Their bifunctional activities were verified in both the electrochemical oxygen evolution reaction (OER) and in the electrochemical reduction of toxic inorganic heavy metal ions [Cr(vi)] in polluted water. The materials showed robust catalytic ability in the oxygen evolution reaction with minimum possible over potential (345 and 350 mV @ η10) as determined by linear sweep voltammetry and the lower Tafel values (52.4 and 84.5 mV dec⁻¹) for Co_0.8Fe_0.2Se₂ and Co_0.8Fe_0.2S₂ respectively. Surprisingly, both the materials also showed an excellent activity towards electrochemical Cr(vi) reduction to Cr(iii). Besides the maximum current achieved for Co_0.8Fe_0.2S₂, a minimum value for the Limit of detection (LOD) was obtained for Co_0.8Fe_0.2S₂ (0.159 μg L⁻¹) compared to Co_0.8Fe_0.2Se₂ (0.196 μg L⁻¹). We tested the durability of catalysts, the critical factor for the prolonged use of catalysts, through the recyclability measurements of these materials as catalysts. Both the catalysts presented outstanding durability and balanced electro catalytic activities for up to 1500 CV cycles, and chronoamperometry studies also confirmed exceptional stability. The enhanced catalytic activities of these materials are ascribed to the free electron movement, evidenced by the increased TPC measured and EIS. Therefore, the template-free synthesis of these electro catalysts containing non-noble metal illustrates the practical approach to develop such types of catalysts for multiple functions.

The ease of production of materials and showing multiple applications are appealing in this modern era of advanced technology. Cobalt–iron chalcogenides showing multiple application is reported.

Ag nanoparticles anchored on NiO octahedrons (Ag/NiO composite): An efficient catalyst for reduction of nitro substituted phenols and colouring dyes

The development of an efficient sustainable catalyst for effective removal of hazardous chemicals, viz. nitrophenols and organic dyes, from wastewater is a challenging task. Herein, facile synthesis of Ag/NiO composites by anchoring Ag nanoparticles (NPs) on NiO octahedrons with different amounts of Ag NPs (AN-5% (5% Ag), AN-10% (10% Ag) and AN-15% (15% Ag)) has been demonstrated. SEM (scanning electron microscopic) and TEM (transmission electron spectroscopic) images ensured the proper anchoring of spherical Ag NPs (particle size = 16.54 ± 1.88 nm) on octahedron particles of NiO, which was also ensured by XPS (X-ray photoelectron spectroscopy) analysis. Moreover, the resulting composites have an average surface area (49-52 m²g^‒1) and pore size (2.39-2.26 nm). All three synthesized Ag/NiO composites (100 μL) catalyzed the complete reduction of para-np (4-nitrophenol: 0.1587 mM) within 2-3 min in the presence of 0.04 M NaBH₄. Among them, AN-5% has been chosen because of the lowest anchored Ag (5%) to obtain the optimized catalyst's amount (50 μL) and concentration of para-np (0.1587 mM). AN-5% also exhibited excellent catalytic activity towards different nitro substituted phenols, viz. ortho-np (2-nitrophenol), meta-np (3-nitrophenol), para-np (4-nitrophenol) and tri-np (2,4,6-trinitrophenol). AN-5% displayed ∼100% catalytic efficiency for reducing meta-np in 2 min with the apparent first order rate constant (k_app) and normalized rate constant (K_nor) as 1.99 s^-1 and 398.14 s^-1 g^-1, respectively. Additionally, AN-5% (29.41 μg mL^-1) reduced >95% of the colouring dyes (10 ppm) such as CONG-R (congo red: 95% in 6 min), METH-O (methyl orange: 97.5% in 7 min), METH-B (methylene blue: 98.3% in 10 min) and RHOD-B (rhodamine B: 99.2% in 5 min). AN-5% not only demonstrated catalytic reduction towards individual pollutants, but also showed excellent activity for reduction of the mixtures of nitrophenols/dyes and for treatment of simulated industrial effluent samples (EFF1, EFF2) and a real industrial sample (textile dye-bath effluent). AN-5% can also be reused up to several cycles with almost same efficiency and followed the Langmuir-Hinshelwood apparent first order kinetics model.

Self-Supporting g-C3N4 Nanosheets/Ag Nanoparticles Embedded onto Polyester Fabric as “Dip-Catalyst” for Synergic 4-Nitrophenol Hydrogenation

Herein, we report the design of a cost-effective catalyst with excellent recyclability, simple recuperation and facile recovery, and the examination between the reaction cycles via the development of self-supporting g-C3N4 nanosheets/Ag NPs polyester fabric (PES) using a simple, facile and efficient approach. PES fabrics were coated via a sono-coating method with carbon nitride nanosheets (GCNN) along with an in situ setting of Ag nanoparticles on PES coated GCNN surface producing PES-GCNN/Ag0. The elaborated textile-based materials were fully characterized using FTIR, 13C NMR, XRD, TGA, SEM, EDX, etc. Catalytic performance of the designed “Dip-Catalyst” demonstrated that the as-prepared PES-GCCN/Ag0 has effectively catalyzed the hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of NaBH4. The 3 × 3 cm2 PES-GCNN/Ag0 showed the best catalytic activity, displaying an apparent rate constant (Kapp) equal to 0.43 min−1 and more than 10 reusability cycles, suggesting that the prepared catalyst-based PES fabric can be a strong nominee for sustainable chemical catalysis. Moreover, the coated fabrics exhibited appreciable antibacterial capacity against Staphylococcus epidermidis (S. epidermidis) and Escherichia coli (E. coli). The present study opens up new opportunities for the future design of a low cost and large-scale process of functional fabrics.

MoS2 nanosheets/silver nanoparticles anchored onto textile fabric as "dip catalyst" for synergistic p-nitrophenol hydrogenation

Attaining a synergistic merge between the performance of homogenous catalysts and the recyclability of heterogeneous catalysts remains until now a concerning issue. The main challenge is to design efficient, low-cost catalyst with outstanding reusability, facile recovery, and ease of retrieval and monitoring between the reuses. Despite the vast efforts in the development of silver nanoparticle-based catalyst for the reaction of hydrogenation of 4-nitrophenol, the aforementioned criteria are infrequently found in a chosen system. Herein, we report a MoS₂ nanosheet/silver nanoparticle-anchored PES-based textile as an efficient and recyclable "dip catalyst" for the 4-NP hydrogenation in the presence of sodium bohydride as model reaction. The textile fabric-based catalyst was processed via a simple sono-coating approach using MoS₂ nanosheets as first coating layer followed by an in situ deposition of silver nanoparticles. The "dip catalyst" fabric is rapidly and easily removed from the reaction and then reinserted in the batch system to attain over 10 reaction cycles. Additionally, the produced textile materials were characterized via spectroscopic and microscopic tools such as FTIR, XRD, SEM, and EDX. Moreover, the sources of the high catalytic activity are also discussed and a plausible reaction mechanism is suggested. The present study demonstrates the potential of metal nanoparticle-textile material combination for future applications in chemical sustainable catalysis for environmental remediation purposes.

Tailored functional materials as robust candidates to mitigate pesticides in aqueous matrices-a review

Pesticides are among the top-priority contaminants, which significantly contribute to environmental deterioration. Conventional techniques are not efficient enough to remove pollutants from environmental matrices. The development of functional materials has emerged as promising candidates to remove and degrade pesticides and related hazardous compounds. Furthermore, the nanohybrid materials with unique structural and functional characteristics, such as better material anchorage, mass transfer, electron-hole separation, and charged interaction make them a versatile option to treat and reduce pollutants from aqueous matrices. Herein, we present the current progress in the development of functional materials for the abatement of toxic pesticides. The physicochemical characteristics and pesticide-removal functionalities of various metallic functional materials (e.g., zirconium, zinc, titanium, tungsten, and iron), polymer, and carbon-based materials are critically discussed with suitable examples. Finally, the industrial-scale applications of the functional materials, concluding remarks, and future directions in this important arena are given.

Silver nanomaterials: synthesis and (electro/photo) catalytic applications

In view of their unique characteristics and properties, silver nanomaterials (Ag NMs) have been used not only in the field of nanomedicine but also for diverse advanced catalytic technologies. In this comprehensive review, light is shed on general synthetic approaches encompassing chemical reduction, sonochemical, microwave, and thermal treatment among the preparative methods for the syntheses of Ag-based NMs and their catalytic applications. Additionally, some of the latest innovative approaches such as continuous flow integrated with MW and other benign approaches have been emphasized that ultimately pave the way for sustainability. Moreover, the potential applications of emerging Ag NMs, including sub nanomaterials and single atoms, in the field of liquid-phase catalysis, photocatalysis, and electrocatalysis as well as a positive role of Ag NMs in catalytic reactions are meticulously summarized. The scientific interest in the synthesis and applications of Ag NMs lies in the integrated benefits of their catalytic activity, selectivity, stability, and recovery. Therefore, the rise and journey of Ag NM-based catalysts will inspire a new generation of chemists to tailor and design robust catalysts that can effectively tackle major environmental challenges and help to replace noble metals in advanced catalytic applications. This overview concludes by providing future perspectives on the research into Ag NMs in the arena of electrocatalysis and photocatalysis.

Immobilizing of palladium on melamine functionalized magnetic chitosan beads: A versatile catalyst for p-nitrophenol reduction and Suzuki reaction in aqueous medium

In this study, an environmental-friendly palladium catalyst with high efficiency, magnetic, recoverability, reusability, and excellent stability was prepared and thoroughly characterized by the Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), X-ray diffraction (XRD), Elemental mapping, Thermogravimetric analysis (TGA) and Energy-dispersive X-ray spectroscopy (EDX). Results demonstrates that melamine provides a coordination point on the surface of chitosan microspheres, which provides a platform for the uniform distribution of palladium (II) and combines with palladium (II) firmly to avoid unnecessary leaching of nanoparticles. Besides, Fe₃O₄/CS-Me@Pd microcapsules exhibited high catalytic performance in reducing p-NP in water at room temperature (150-300 s). This composite was also effective in the Suzuki-Miyaura coupling reaction under mild conditions with high catalytic performance (TON = 3.8 × 10⁴, TOF = 7.6 × 10⁴). Reproducibility experiments also showed that Fe₃O₄/CS-Me@Pd microcapsules have high recovery efficiency and can work at least six times during these two catalytic reactions. The hot filtration test indicated that the catalyst has heterogeneous nature.

In situ preparation of highly dispersed Pd supported on exfoliated layered double hydroxides via nitrogen plasma for 4-nitrophenol reduction

In this work, a simple and environmental-friendly nitrogen glow discharge plasma reduction method has been developed for synthesizing palladium nanoparticles (PdNPs) supported on exfoliated Mg-Al-layered double hydroxide (Pd/LDH) catalysts. The as-prepared catalysts were characterized by means of characterizations methods, which contain X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectrometry (XPS), and Fourier transform infrared (FT-IR). Highly dispersed ultrafine PdNPs were supported on exfoliated, defect-induced LDHs uniformly without agglomeration. The effects of treatment time of nitrogen plasma and Pd loading amount on structure, morphology, and catalytic performance of Pd/LDHs were investigated. The comparisons of structure and morphology between LDHs and Pd/LDHs were also discussed. The average particle size of as-synthesized PdNPs with face-centered cubic structure is 2.01 nm, which ranges from 1.18 to 3.01 nm. Nitrogen plasma cannot only reduce Pd²⁺, but also exfoliate LDHs, introduce defects, and even destroy the structure of LDHs. The Pd/LDH catalyst with 1 wt% Pd loading under nitrogen plasma treatment for 60 min showed the best catalytic performance in 4-nitrophenol reduction. The turnover frequency (TOF) of as-prepared catalyst is 20-fold higher than that of commercial Pd/C catalyst.

Synthesis of CaFe2O4-NGO Nanocomposite for Effective Removal of Heavy Metal Ion and Photocatalytic Degradation of Organic Pollutants

This paper reports the successful synthesis of magnetic nanocomposite of calcium ferrite with nitrogen doped graphene oxide (CaFe2O4-NGO) for the effective removal of Pb(II) ions and photocatalytic degradation of congo red and p-nitrophenol. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), and scanning electron microscopy-energy dispersive X-ray (SEM-EDX) techniques confirmed the presence of NGO and CaFe2O4 in the nanocomposite. The Mössbauer studies depicted the presence of paramagnetic doublet and sextet due to presence of CaFe2O4 NPs in the nanocomposite. The higher BET surface area in case of CaFe2O4-NGO (52.86 m2/g) as compared to CaFe2O4 NPs (23.45 m2/g) was ascribed to the effective modulation of surface in the presence of NGO. Adsorption followed the Langmuir model with maximum adsorption capacity of 780.5 mg/g for Pb(II) ions. Photoluminescence spectrum of nanocomposite displayed four-fold decrease in the intensity, as compared to ferrite NPs, thus confirming its high light capturing potential and enhanced photocatalytic activity. The presence of NGO in nanocomposite offered an excellent visible light driven photocatalytic performance. The quenching experiments supported ●OH and O2●- radicals as the main reactive species involved in carrying out the catalytic system. The presence of Pb(II) had synergistic effect on photocatalytic degradation of pollutants. This study highlights the synthesis of CaFe2O4-NGO nanocomposite as an efficient adsorbent and photocatalyst for remediating pollutants.

A reusable catalyst based on CuO hexapods and a CuO-Ag composite for the highly efficient reduction of nitrophenols

The enormous and urgent need to explore cost-effective catalysts with high efficiency has always been at the forefront of environmental protection and remediation research. This work develops a novel strategy for the fabrication of reusable CuO-based non-noble metal nanomaterials as high-efficiency catalysts. We report a facile and eco-friendly synthesis of CuO hexapods and CuO–Ag composite using uric acid as a reductant and protectant. Both exhibited high catalytic activity in the hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride (NaBH₄), with the CuO–Ag composite showing superior catalytic performance. Notably, the highest turnover frequency of CuO–Ag reached 7.97 × 10⁻² s⁻¹, which was much higher than numerous noble-metal nanomaterials. In addition, CuO hexapods and CuO–Ag composite were also shown to act as highly efficient and recyclable catalysts in the degeneration of 4-NP. Both CuO hexapods and the CuO–Ag composite exhibited outstanding catalytic durability, with no significant loss of activity over more than 10 cycles in the hydrogenation of 4-NP.

Schematic illustration for the process of preparing CuO hexapods and CuO–Ag composite, and their application in catalytically reducing 4-NP and K₃(Fe(CN)₆).

Intriguing hierarchical Co@NC microflowers in situ assembled by nanoneedles: Towards enhanced reduction of nitroaromatic compounds via interfacial synergistic catalysis

Developing highly efficient and cost-effective catalyst with tuned microstructure holds great promise in the reduction of nitroaromatic compounds under mild reaction conditions. Herein, we report a new Co@NC-MF catalyst with a fascinating hierarchical flower-like architecture in situ assembled from uniform Co@NC nanoneedles, which can function as a favorable platform for the efficient reduction of nitroaromatic compounds in the presence of NaBH₄. In addition with the structural advantage, the characterization and experimental results demonstrate the enormous advantage of interfacial synergistic catalysis in enhancing the catalytic performance. The outside electron-rich N-doped carbon layer as Lewis basic sites and the inside Co nanoparticles are responsible for the adsorption of 4-nitrophenol (4-NP) and generation of active hydrogen species, respectively. This work contributes to the construction of well-integrated composites with well-balanced interface synergy to boost the catalytic performance in various heterogeneous reactions.

Ranolazine-functionalized CuO NPs: efficient homogeneous and heterogeneous catalysts for reduction of 4-nitrophenol

In the present study copper oxide nanoparticles (CuO NPs) were synthesized using a hydrothermal method with ranolazine as a shape-directing agent. Ranolazine-functionalized CuO NPs were characterized by various analytical techniques such as scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). The SEM pattern confirmed the morphology of ranolazine-functionalized CuO NPs with well-defined rice-like structures. FTIR spectroscopy confirmed the interaction between CuO NPs and ranolazine. The XRD analysis indicated that the structure of ranolazine-functionalized CuO NPs was monoclinic crystalline and the size ranged between 9 and 18 nm with an average particle size of 12 nm. The smaller size range of CuO NPs gave a large surface area that enhanced the efficiency of these catalysts employed for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the H ₂ O system. In homogeneous catalysis, results showed that 50 μL of CuO NPs was required in the presence of NaBH4 for 99% reduction of 4-NP in 240 s. On the other hand, for heterogeneous catalysis, 0.5 mg of CuO NPs was used in the presence of NaBH4 for 99% catalytic reduction of 4-NP to 4-AP in 320 s. The rate of reaction for homogeneous catalysis and heterogeneous catalysis was determined from the plots of In(Ct /C0) of 4-NP versus time (s), which showed good linearity with values of 1.3 × 10 ^-2 and 8.8 × 10 ^-3 s ^-1 . respectively. The high-quality catalytic efficiency, good reusability, nontoxic nature, and low cost are favorable properties of the synthesized CuO NPs for use as efficient catalysts for reduction of 4-AP to 4-NP in both homogeneous and heterogeneous media.

Biochemical synthesis of palladium nanoparticles: The influence of chemical fixatives used in electron microscopy on nanoparticle formation and catalytic performance

Palladium nanoparticles (PdNPs) can catalyse a range of reductive chemical reactions transforming both organic and inorganic environmental pollutants. PdNPs that ranged from <2 to 2-40 nm were synthesized using chemical methods, and bacterial biomass with/without chemical fixatives. PdNP formation was enhanced by adsorption of Pd(II) to bacterial biomass, followed by fixation with formate or glutaraldehyde. TEM-SAED analyses confirmed that the cell associated PdNPs were polycrystalline with a face-centered cubic structure. Chemically formed PdNPs possessed a higher Pd(0):Pd(II) ratio and produced structurally similar nanoparticles as the biotic systems. These PdNPs were employed to catalyze two, reductive chemical reactions, transforming 4-nitrophenol (4-NP) and hexavalent chromium [Cr(VI)], into 4-aminophenol and Cr(IV), respectively. In the reduction of 4-NP, the catalytic performance was directly proportional to PdNP surface area, i.e., the smallest PdNPs in formate-PdCH34 cells had the fastest rate of reaction. The mass of Pd(0) as PdNPs was the main contributor to Cr(VI) reduction; the chemically synthesized PdNPs showed the highest removal efficiency with 96% at 20 min. The use of glutaraldehyde enhanced the reduction of Pd(II) and promoted PdNPs formation, i.e., creating an artefact of fixation; however, this treatment also enhanced the catalytic performance of these PdNPs.

Physiological and anti-oxidative response of biologically and chemically synthesized iron oxide: Zea mays a case study

The synthesis methodology, particle size and shape, dose optimization, and toxicity studies of nano-fertilizers are vital prior to their field application. This study investigates the comparative response of chemically synthesized and biologically synthesized iron oxide nanorods (NRs) using moringa olefera along with bulk FeCl3 on summer maize (Zea mays). It is found that FeCl3 salt and chemically synthesized iron oxides NRs caused growth retardation and impaired plant physiological and anti-oxidative activities at a concentration higher than 25 mg/L due to toxicity by over accumulation. While iron released form biologically synthesized NRs have shown significantly positive results even at 50 mg/L due to their low toxicity, an improved leaf area (13%), number of leaves per plant (26%), total chlorophyll content (80%) and nitrate content (6%) with biologically synthesized NRs are obtained. Moreover, the plant anti-oxidative activity also increased on treatment with biologically synthesized NRs because of their ability to form a complex with metal ions. These findings suggest that biologically synthesized iron oxides NRs are an efficient iron source and can last for a long time. Thus, proving that nanofertilizer are required to have specific surface chemistry to release the nutrient in an appropriate concentration for better plant growth.

In situ immobilization of ultra-fine Ag NPs onto magnetic Ag@RF@Fe3O4 core-satellite nanocomposites for the rapid catalytic reduction of nitrophenols

Novel magnetic Ag@RF@Fe₃O₄ core-satellite (MCS) nanocomposites were prepared through in situ photoreduction upon bridging Fe(III) and Ag⁺ via hydroxyl groups in resorcinol formaldehyde (RF) resin by virtue of the coordination effect. The catalytic activity of MCS nanocomposites was evaluated based on catalytic 4-nitrophenol (4-NP) reduction with NaBH₄ as the reducing agent. It was noteworthy that the MCS-3 was beneficial to obtain a superior reaction rate constant of 2.27 min^-1 and a TOF up to 72.7 h^-1. Moreover, the MCS could be easily recovered by applying an external magnetic field and was reused for five times without significantly decrease in catalytic activity. Kinetic and thermodynamic study revealed that catalytic 4-NP reduction using MCS nanocatalysts obeyed the Langmuir-Hinshelwood mechanism and was controlled by the diffusion rate of substrates. Overall, the immobilization of ultra-fine Ag nanoparticles and the extremely negative potentials around MCS nanocomposites, which were effective for the diffusion of reactants, synergistically accelerated the catalytic reduction reactions.

An ultrasonic-assisted synthesis of leather-derived luminescent graphene quantum dots: catalytic reduction and switch on-off probe for nitro-explosives

The current research effort demonstrates the ultrasonic-assisted synthesis of highly fluorescent graphene quantum dots (GQDs) of ∼5 nm diameter. First, acid pyrolysis with ultrasonic hydrothermal co-cutting breaks down the coarse graphite into nanometric graphene sheets (GS) and graphene oxide sheets (GOS) with oxygen-rich functionalities. These functionalities were then used to break GOS into graphene oxide nanofibers (GONFs) and graphene oxide quantum dots (GOQDs). Finally, upon reduction, GOQDs lose oxygen linkages to produce fluorescent GQDs (quantum yield up to 27%). The as-developed GQDs were characterized with detailed optical and spectral studies through UV, PL, FTIR, TEM, AFM, XPS, XRD and other techniques. Notably, the synthesized GQDs were catalytically active to serve as a ratiometric fluorescence switch on-off probe for the reduction of toxic nitrophenols. Moreover, the GQDs detected nitrophenol derivatives at lower concentrations than previously reported analytical values. During the real sample analysis of spiked industrial water and exposed soil samples, a high selectivity and sensitivity of the applied method was achieved with a recovery of 99.7% to 101.3% at spiked concentrations of 400 nM to 100 nM, respectively. The detection limit of the photoluminescent probe for paranitrophenol was as low as 10 pM.

Can Plasmonic Effect Cause an Increase in the Catalytic Reduction of p-nitrophenol by Sodium Borohydride over Au Nanorods?

The catalytic reduction of p-nitrophenol (4-NP) to 4-aminopyridine (4-AP) over Au nanoparticles can be increased by light illumination. Whether this is caused by the plasmonic effect remains unclear. The present research carried out a careful examination of the effects of light illumination and temperature on the catalytic conversion of 4-NP to 4-AP over Au nanorods. It was seen that light illumination has no effect on the apparent activation energy; this indicates that the catalytic mechanism is unchanged and the activity increase cannot be attributed to the effect of hot electrons. Based on the simulation of finite-difference time domain, the theoretical analysis also showed that plasmonic heating cannot play a major role. Thermographic mapping showed that the temperature of water solutions shows an increase under light illumination. By taking this temperature increase into consideration, the light-induced increase of the 4-NP to 4-AP conversion can agree well with dark catalysis, which cannot be attributed to the plasmonic effects of the Au nanorods.