Stable Ni nanoparticle-reduced graphene oxide composites for the reduction of highly toxic aqueous Cr(VI) at room temperature

Pd nanoparticles embedded in nanolignin (Pd@LNP) as a water dispersible catalytic nanoreactor for Cr(VI), 4-nitrophenol reduction and CC coupling reactions

The use of water-dispersible and sustainable Pd nanocatalysts to reduce toxic heavy metal ions and catalyze important organic reactions has profound significance for the environmental remediation and the catalytic industry. In this work, a novel water-dispersible and recyclable Pd@LNPs nanoreactor composed of Pd nanoparticle cluster core and LNPs shell was developed in microwave reactor in aqueous solution. It turned out that Pd nanoparticles grew uniformly and stably inside LNPs nanosphere due to the coordinated binding and interaction between Pd and the functional groups in LNPs, which was significantly different from surface loading. The green and biodegradable LNPs nanospheres are not only used as reducing agents for Pd (II) and nanocarriers, but also act as individual nanocontainers to provide favorable sites for reactions and effectively control the entry and release of reactants and products. Furthermore, the excellent and efficient catalytic properties of Pd@LNPs were exhibited by CC coupling reactions and the reduction of Cr(VI) and 4-nitrophenol. The Pd@LNPs prepared in this study have the advantages of excellent dispersion, great recyclability, high turnover frequency and better green sustainability metrics. It will have a great significance for the development of the potential high-value of lignin and the progress in the field of bio-nanocatalysts.

Microwave-Assisted Synthesis of Pd Nanoparticles into Wood Block (Pd@wood) as Efficient Catalyst for 4-Nitrophenol and Cr(VI) Reduction

Palladium (Pd) nanoparticle catalysis has attracted increasing attention due to its efficient catalytic activity and its wide application in environmental protection and chemical synthesis. In this work, Pd nanoparticles (about 71 nm) were synthesized in aqueous solution by microwave-assisted thermal synthesis and immobilized in beech wood blocks as Pd@wood catalysts. The wood blocks were first hydrothermally treated with 10% NaOH solution to improve the internal structure and increase their porosity, thereby providing favorable attachment sites for the formed Pd nanoparticles. The stable deposition of Pd nanoparticle clusters on the internal channels of the wood blocks can be clearly observed. In addition, the catalytic performance of the prepared Pd@wood was investigated through two model reactions: the reduction of 4-nitrophenol and Cr(VI). The Pd@wood catalyst showed 95.4 g-1 s-1 M-1 of normalized rate constant knorm and 2.03 min-1 of the TOF, respectively. Furthermore, Pd nanoparticles are integrated into the internal structure of wood blocks by microwave-assisted thermal synthesis, which is an effective method for wood functionalization. It benefits metal nanoparticle catalysis in the synthesis of fine chemicals as well as in industrial wastewater treatment.

Electrospun Carbon Nanofibers and Their Applications in Several Areas

Carbon nanofibers (CNFs) have a broad spectrum of applications, including sensor manufacturing, electrochemical catalysis, and energy storage. Among different manufacturing methods, electrospinning, due to its simplicity and efficiency, has emerged as one of the most powerful commercial large-scale production techniques. Numerous researchers have been attracted to improving the performance of CNFs and exploring new potential applications. This paper first discusses the working theory of manufacturing electrospun CNFs. Next, the current efforts in upgrading the properties of CNFs, such as pore architecture, anisotropy, electrochemistry, and hydrophilicity, are discussed. The corresponding applications due to the superior performances of CNFs are subsequently elaborated. Finally, the future development of CNFs is discussed.

Magnetically Stimulable Graphene Oxide/Polypropylene Nanocomposites

Core-shell magnetic air-stable nanoparticles have attracted increasing interest in recent years. Attaining a satisfactory distribution of magnetic nanoparticles (MNPs) in polymeric matrices is difficult due to magnetically induced aggregation, and supporting the MNPs on a nonmagnetic core-shell is a well-established strategy. In order to obtain magnetically active polypropylene (PP) nanocomposites by melt mixing, the thermal reduction of graphene oxides (TrGO) at two different temperatures (600 and 1000 °C) was carried out, and, subsequently, metallic nanoparticles (Co or Ni) were dispersed on them. The XRD patterns of the nanoparticles show the characteristic peaks of the graphene, Co, and Ni nanoparticles, where the estimated sizes of Ni and Co were 3.59 and 4.25 nm, respectively. The Raman spectroscopy presents typical D and G bands of graphene materials as well as the corresponding peaks of Ni and Co nanoparticles. Elemental and surface area studies show that the carbon content and surface area increase with thermal reduction, as expected, following a reduction in the surface area by the support of MNPs. Atomic absorption spectroscopy demonstrates about 9-12 wt % metallic nanoparticles supported on the TrGO surface, showing that the reduction of GO at two different temperatures has no significant effect on the support of metallic nanoparticles. Fourier transform infrared (FT-IR) spectroscopy shows that the addition of a filler does not alter the chemical structure of the polymer. Scanning electron microscopy of the fracture interface of the samples demonstrates consistent dispersion of the filler in the polymer. The TGA analysis shows that, with the incorporation of the filler, the initial (T_onset) and maximum (T_max) degradation temperatures of the PP nanocomposites increase up to 34 and 19 °C, respectively. The DSC results present an improvement in the crystallization temperature and percent crystallinity. The filler addition slightly enhances the elastic modulus of the nanocomposites. The results of the water contact angle confirm that the prepared nanocomposites are hydrophilic. Importantly, the diamagnetic matrix is transformed into a ferromagnetic one with the addition of the magnetic filler.

Reduced graphene Oxide/NiO based nano-composites for the efficient removal of alizarin dye, indigo dye and reduction of nitro aromatic compounds

Removal of alizarin red S (ARS) and Indigo dye from aqueous media and reduction of nitro aromatic compounds are successfully done under mild condition by using reduced Graphene Oxide-Nickel Oxide (rGO-NiO) nanocomposite as catalyst. RGO-NiO is well characterized by different analytical techniques. Morphology, structural, and composition studies done by HRTEM, FESEM, EDX, TGA, FTIR, XPS, Raman spectroscopy, and XRD. RGO-NiO nanocomposite has high stability for the removal of ARS, Indigo dye, reduction reaction nitro aromatic compounds.

Noncovalent Assembly and Catalytic Activity of Hybrid Materials Based on Pd Complexes Adsorbed on Multiwalled Carbon Nanotubes, Graphene, and Graphene Nanoplatelets

Green catalysts with excellent performance in Cu-free Sonogashira coupling reactions can be prepared by the supramolecular decoration of graphene surfaces with Pd(II) complexes. Here we report the synthesis, characterization, and catalytic properties of new catalysts obtained by the surface decoration of multiwalled carbon nanotubes (MWCNTs), graphene (G), and graphene nanoplatelets (GNPTs) with Pd(II) complexes of tetraaza-macrocyclic ligands bearing one or two anchor functionalities. The decoration of these carbon surfaces takes place under environmentally friendly conditions (water, room temperature, aerobic) in two steps: (i) π–π stacking attachment of the ligand via electron-poor anchor group 6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxo-pyrimidine and (ii) Pd(II) coordination from PdCl₄^2–. Ligands are more efficiently adsorbed on the flat surfaces of G and GNPTs than on the curved surfaces of MWCNTs. All catalysts work very efficiently under mild conditions (50 °C, aerobic, 7 h), giving a similar high yield (90% or greater) in the coupling of iodobenzene with phenylacetylene to form diphenylacetylene in one catalytic cycle, but catalysts based on G and GNPTs (especially on GNPTs) provide greater catalytic efficiency in reuse (four cycles). The study also revealed that the active centers of the ligand-Pd type decorating the support surfaces are much more efficient than the Pd(0) and PdCl₄^2– centers sharing the same surfaces. All of the results allow a better understanding of the structural factors to be controlled in order to obtain an optimal efficiency from similar catalysts based on graphene supports.

Green catalysts with high efficiency in the Cu-free Sonogashira C−C coupling reactions can be prepared by the supramolecular functionalization of carbon materials.

Metallic nanoparticles for catalytic reduction of toxic hexavalent chromium from aqueous medium: A state-of-the-art review

The ever increasing concentration of toxic and carcinogenic hexavalent chromium (Cr (VI)) in various environmental mediums including water-bodies due to anthropogenic activities with rapid civilization and industrialization have become the major issue throughout the globe during last few decades. Therefore, developing new strategies for the treatment of Cr(VI) contaminated wastewaters are in great demand and have become a topical issue in academia and industry. To date, various techniques have been used for the remediation of Cr(VI) contaminated wastewaters including solvent extraction, adsorption, catalytic reduction, membrane filtration, biological treatment, coagulation, ion exchange and photo-catalytic reduction. Among these methods, the transformation of highly toxic Cr(VI) to benign Cr(III) catalyzed by metallic nanoparticles (M-NPs) with reductant has gained increasing attention in the past few years, and is considered to be an effective approach due to the superior catalytic performance of M-NPs. Thus, it is a timely topic to review this emerging technique for Cr(VI) reduction. Herein, recent development in synthesis of M-NPs based non-supported, supported, mono-, bi- and ternary M-NPs catalysts, their characterization and performance for the reduction of Cr(VI) to Cr(III) are reviewed. The role of supporting host to stabilize the M-NPs and leading to enhance the reduction of Cr(VI) are discussed. The Cr(VI) reduction mechanism, kinetics, and factors affecting the kinetics are overviewed to collect the wealthy kinetics data. Finally, the challenges and perspective in Cr(VI) reduction catalyzed by M-NPs are proposed. We believe that this review will assist the researchers who are working to develop novel M-NPs catalysts for the reduction of Cr(VI).

Treated activated carbon as a metal-free catalyst for effectively catalytic reduction of toxic hexavalent chromium

In this work, activated carbon treated in N₂ atmosphere, as a non-metallic catalyst, exhibits excellent catalytic performance in reduction of Cr (VI) to Cr (III) using HCOOH as the reducing agent at room temperature. A series of characterizations and control experiments were carried out to deduce the possible reaction mechanism. The results showed that the improved catalytic performance can be attributed to the enhanced graphitization degree and basic sites such as pyrone-like, which favor electron transferring and activation of reactant. The reaction rate constant observed herein for the C-800 was 22 and 6 times more than that for C-0 and Pd/C catalyst, respectively. In addition, C-800 showed good recycle performance, and no loss of activity was observed after 5 cycles. This study broadens the application of nonmetallic catalyst and provides an easy-available and cost-effective catalytic material for removing toxic Cr (VI).

MXene quantum dots decorated Ni nanoflowers for efficient Cr (VI) reduction

Nickel@MXene quantum dots (Ni@MQDs), as novel flower-like hybrid materials, were firstly prepared through a simple reduction method. The Ni@MQDs exhibited an outstanding catalytic performance for Cr (VI) reduction with a low activation energy (E_a = 18.9 kJ mol^-1) and a high kinetic constant (k = 0.4779 min^-1) in the presence of formic acid (HCOOH). Density functional theory calculations demonstrated that Ni@MQDs exhibited an upshift of d-band center of active Ni atoms to promote the adsorption of both HCOOH and active H atoms, as well as an improved conductivity to boost the catalytic reaction kinetics, leading to the most favorable catalytic performance. This work may open up a new avenue towards the design and synthesis of novel MQDs-based hybrid catalysts for wastewater treatment.

Visible-light-driven sonophotocatalysis for enhanced Cr(VI) reduction based on mixed-linker zirconium-porphyrin MOFs

In this study, we synthesized and characterized two mixed-linker zirconium-porphyrin metal-organic frameworks, PCN-134 and PCN-138 which constructed from tetratopic light harvesting TCPP ligand and tritopic BTB/TBTB ligand (TCPP = trakis(4-carboxyphenyl)porphyrin),...

Catalytic reduction of in-flow aqueous Cr(vi) using a slurry of activated carbon fiber-supported Ni nanoparticles in a coiled flow inverter

CFI technology is utilized for the in-flow reduction of Cr(vi) using formic acid as the reducing agent and an aqueous dispersion of Ni/ACF, as an alternative to the conventional packed bed reactors.

Nitrogen-doped lignin-derived carbon for catalytic reduction of hexavalent chromium via HCOOH-mediated hydrogenation

It is highly desirable to explore efficient catalysts for reducing toxic Cr⁶⁺ to benign Cr³⁺ under mild and eco-friendly conditions. This article describes a facile fabrication of nitrogen doped carbon (N@C-g-C₃N₄) as a metal-free catalyst for Cr⁶⁺ reduction using lignin as a carbon source and g-C₃N₄ nanosheets as a nitrogen source. The structural properties of the N@C-g-C₃N₄ catalyst are characterized by TEM, HR-TEM, XRD, TGA, Raman, EDS-mapping, XPS and BET techniques. The summation of these analyses sheds light on the high surface area (903 m² g⁻¹), mesopore size (17.3 nm) and defects (I_D/I_G = 0.97) of N@C-g-C₃N₄, which contribute to its excellent catalytic activity in HCOOH-mediated reduction of Cr⁶⁺ to Cr³⁺ with high rate constant (2.98 min⁻¹) and turnover frequency (2.21 mol_K2Cr2O7 g_catalyst⁻¹ min⁻¹) and complete degradation (100%) within 5 min. The catalytic performance of the catalyst reveals that the reduction activity is significantly dependent on the concentration of Cr⁶⁺ and HCOOH, catalyst loading, pH, temperature, and foreign ions. Particularly, the N@C-g-C₃N₄ catalyst shows superior stability and renewability with little loss of activity (≥95%) after 8 months storage and five repeated uses. Furthermore, N@C-g-C₃N₄ can be applied in other hydrogenation reactions involving K₃[Fe(CN)₆], 4-NP and BPA using NaBH₄ as a hydrogen donor, and the removal of organic dyes. These findings illustrate that N@C-g-C₃N₄ as a metal-free catalyst is effective, versatile and eco-friendly for the reduction of Cr⁶⁺ from contaminated environments.

Lignin-derived carbon doped with nitrogen for Cr⁶⁺ reduction through HCOOH-mediated hydrogenation in mild conditions.

Self-Assembled Silver Nanoparticles Decorated on Exfoliated Graphitic Carbon Nitride/Carbon Sphere Nanocomposites as a Novel Catalyst for Catalytic Reduction of Cr(VI) to Cr(III) from Wastewater and Reuse for Photocatalytic Applications

Silver nanoparticles decorated on an exfoliated graphitic carbon nitride/carbon sphere (AgNP/Eg-C₃N₄/CS) nanocomposites were synthesized by an adsorption method with a self-assembled process. These nanoparticles were characterized by different techniques like UV-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Raman spectroscopy, scanning electron spectroscopy (SEM), transmission electron spectroscopy (TEM), electrochemical impedance spectroscopy (EIS), and ζ potential. AgNP/Eg-C₃N₄/CS nanocomposites showed a higher catalytic reduction activity for the conversion of Cr(VI) into Cr(III) with formic acid (FA) at 45 °C when compared to bulk graphitic carbon nitride (Bg-C₃N₄, Eg-C₃N₄, CS, and Eg-C₃N₄/CS). The kinetic rate constants were determined as a function of catalyst dosage, concentration of Cr(VI), pH, and temperature for the AgNP/Eg-C₃N₄/CS nanocomposite. This material showed higher reduction efficiency (98.5%, k = 0.0621 min^-1) with turnover frequency (0.0158 min^-1) for the reduction of Cr(VI) to Cr(III). It also showed great selectivity and high stability after six repeated cycles (98.5%). Further, the reusability of the Cr(III)-AgNP/Eg-C₃N₄/CS nanocomposite was also investigated for the photocatalytic degradation of methylene blue (MB) under visible light irradiation with various time intervals and it showed good degradation efficiency (α = 97.95%). From these results, the AgNP/Eg-C₃N₄/CS nanocomposite demonstrated higher catalytic activity, improved environmental friendliness, lower cost for the conversion of toxic Cr(VI) to Cr(III) in solutions, and also good reusability.

Sub-level engineering strategy of nitrogen-induced Bi2O3/g-C3N4: a versatile photocatalyst for oxidation and reduction

Herein, the α-Bi₂O₃ nanocrystal decorated by nitrogen dopant and its heterojunction nanocomposite with g-C₃N₄ (N_0.1/Bi₂O₃/g-C₃N₄) is successfully fabricated for the first time, for photo-oxidation of RhB and photo-reduction of Cr(VI) to Cr(III). The resulting N_0.1/Bi₂O₃/g-C₃N₄ (3%) nanocomposite showed an optimal Cr(VI) photo-reduction and RhB photo-oxidation rates under visible-light irradiation, being 3-4 times higher than that of pure α-Bi₂O₃. The results from XPS confirmed the substitution of nitrogen with various oxidation states from N³⁺ to N^x+ (x < 5), due to the existence of different nitrogen oxides including N-O, O-N=O, and NO₃^- in the crystal structure. We investigated the reaction mechanism using catalytic tests, impedance spectroscopy, EPR technique, and density functional calculations. The DFT calculations presented the appearance of a new mid-gap hybrid of p states, comprised of N 2p, O 2p, and Bi 6P states, which enhance light absorption capacity and narrow band gap. The theoretical results were in excellent agreement with experimental UV-Vis data. The N_0.1/Bi₂O₃/g-C₃N₄ nanocomposite exhibited acceptable practical application value and recycling ability for removal of the contaminants. Such improved photocatalytic activity is originated from the modified band positions, new electron evolution pathway, introducing defects in α-Bi₂O₃ by insertion of N atoms into the Bi sites, and the enhanced charge carrier mobility between N_0.1/Bi₂O₃ and g-C₃N₄. The strategy to form nitrogen-doped bismuth-based nanocomposites may open a new opportunity to design atomic-level electronic defects by feasible methods to obtain a versatile photocatalyst material with simultaneous photo-reduction and photo-oxidation ability for removal of Cr(VI) and organic dyes from water.

Interconnected hierarchical nickel-carbon hybrids assembled by porous nanosheets for Cr(VI) reduction with formic acid

Magnetic carbon materials promise distinct advantages in the decontamination of heavy metal ions. In this work, a novel interconnected hierarchical nickel-carbon (Ni@IHC) hybrid was synthesized by combining the solvothermal method with a one-step pyrolysis under argon atmosphere. Benefitting from 3D flower-like morphology, interconnected porous nanosheets, large surface area, and abundant Ni nanoparticles, Ni@IHC hybrids can remove Cr(VI) within 25 min by using formic acid (FA) as a reductant at 25 ℃. Furthermore, the experimental parameters that can affect the material catalytic performance such as initial Cr(VI) concentration, catalyst dosage, FA concentration, and temperature were also investigated in detail. It was found that highly dispersed Ni nanoparticles contributed significantly to the reduction process. More importantly, the embedded Ni nanoparticles favor fast separation by a magnet and were helpful for the recycles use. This Ni@IHC hybrid was obtained by a facile and easy scale-up method, resulting in the fast transformation of Cr(VI) into Cr(III).

Efficient catalytic reduction of highly toxic aqueous Cr(VI) with Fe@CBC/Pd composites at room temperature

We report a facile approach to fabricating catalytic active palladium nanoparticles (NPs) immobilized on Fe-loaded carbonized bacterial cellulose nanofibers (Fe@CBC) for the catalytic reduction of toxic Cr(VI) to Cr(III) at room temperature. The formed nanofiber composites (Fe@CBC/Pd) was investigated by various physicochemical characterization and its catalytic activity, and reusability were evaluated as well. The results demonstrated that the Fe@CBC/Pd exhibited favorable catalytic activity for the reduction of Cr(VI) to Cr(III) in the presence of HCOOH. Moreover, the catalyst could be easily recovered from reaction system in a facile manner and recycled four times without obvious loss in activity.

Inorganic nanoparticles for reduction of hexavalent chromium: Physicochemical aspects

Hexavalent Chromium [Cr(VI)] is a highly carcinogenic and toxic material. It is one of the major environmental contaminants in aquatic system. Its removal from aqueous medium is a subject of current research. Various technologies like adsorption, membrane filtration, solvent extraction, coagulation, biological treatment, ion exchange and chemical reduction for removal of Cr(VI) from waste water have been developed. But chemical reduction of Cr(VI) to Cr(III) has attracted a lot of interest in the past few years because, the reduction product [Cr(III)] is one of the essential nutrients for organisms. Various nanoparticles based systems have been designed for conversion of Cr(VI) into Cr(III) which have not been critically reviewed in literature. This review present recent research progress of classification, designing and characterization of various inorganic nanoparticles reported as catalysts/reductants for rapid conversion of Cr(VI) into Cr(III) in aqueous medium. Kinetics and mechanism of nanoparticles enhanced/catalyzed reduction of Cr(VI) and factors affecting the reduction process have been discussed critically. Personal future insights have been also predicted for further development in this area.

An overview of palladium supported on carbon-based materials: Synthesis, characterization, and its catalytic activity for reduction of hexavalent chromium

Palladium plays a pivotal role in most of the industrial heterogeneous catalysts, because of its unique properties such as well-defined structure, great intrinsic carrier, outstanding electronic, mechanical and thermal stability. The combination of palladium and various porous carbons (PCs) can widen the use of heterogeneous catalysts. This review highlights the advantages and limitations of carbon supported palladium-based heterogeneous catalyst in reduction of toxic hexavalent chromium (Cr^(VI)). In addition, we address recent progress on synthesis routes for mono and bimetallic palladium nanoparticles supported by various carbon composites including graphene-based materials, carbon nanotubes, mesoporous carbons, and activated carbons. The related reaction mechanisms for the Cr^(VI) reduction are also suggested. Finally, the challenge and perspective are proposed.

Facile photocatalytic reduction of carcinogenic Cr(vi) on Fe-doped copper sulfide nanostructures

In this study, Fe-doped copper sulfide nanoparticles (NPs) were investigated for the solar-assisted reduction of CrVI ions in raw water. The Fe-doped NPs were synthesized by decomposing copper(ii) N,N-diphenylmethylpiperazinecarbamodithioate via a facile single-step, one-pot solvothermal method in the presence of iron salt. The CrVI photoreduction data were fit to a pseudo-first-order kinetic model and a Langmuir model. The CuS/Cu2S NP reduction ability for CrVI increases with an increase in dopant percentage. The best catalyst (9% Fe-doped) was able to reduce CrVI (10-4 M K2Cr2O7) to CrIII in raw water using an initial amount of 10 mg in 6 min with a reduction efficiency of up to 100%. The photocatalytic activity was examined while varying five different parameters: sunlight, diffused light, change in pH, and changes in the concentration of the catalyst and the temperature. This new approach presents an active, simple, and cost-effective means for wastewater treatment.

Microwave-assisted catalytic conversion of glucose to 5-hydroxymethylfurfural using “three dimensional” graphene oxide hybrid catalysts

High glucose → 5-HMF conversion was yielded with conversion of 99% and yield of 95% by 3D structured NiGO-FD and microwave-assisted reaction.

Biochemical and behavioral responses of zebrafish embryos to magnetic graphene/nickel nanocomposites

Graphene nanocomposites are emerging carbon-based materials with interesting electrical, mechanical, optical and magnetic properties, relevant for applications in different fields. Despite this increased use, the impact of graphene nanocomposites residues in the environment has not been properly studied. Thus, the goal of this work was to assess the toxicity of two nickel/graphene nanocomposites (G/Ni1 and G/Ni2) differing in size and shape to Danio rerio embryos. Their toxicity was evaluated using apical (mortality, development and hatching), biochemical [cholinesterase (ChE), glutathione-S-transferase (GST), and catalase (CAT) activities] and behavioral (locomotor activity) endpoints. At the tested concentrations, neither of the nanocomposites presented lethal or developmental effects. Nevertheless, both nanocomposites induced behavioral effects, reducing swimming distances. This effect was, however detected at lower concentrations in the G/Ni1 nanocomposite. At biochemical level, only G/Ni1 nanocomposite showed to interfere with the measured parameters, increasing the activities of ChE, CAT and GST. Differences in the effects induced by the two nanocomposites seem to be related not only with their size, but also with the shape and the ability to continuously release nickel ions to aqueous medium. This work highlights the importance of studying graphene nanocomposites effects to aquatic organisms even when acute toxicity is not expected. The relevance of the effects found in this work need to be further analyzed in light of the consequences to the long-term fitness of the organisms and in light of the environmental concentrations expected for this type of compounds.

Synthesis of high performance Ni3C-Ni decorated thermally expanded reduced graphene oxide (TErGO/Ni3C-Ni) nanocomposite: A stable catalyst for reduction of Cr(VI) and organic dyes

A high performance thermally expanded reduced graphene oxide (TErGO) nanocomposite decorated with Ni₃C-Ni nanoparticles (TErGO/Ni₃C-Ni) has been successfully synthesized by using a facile and eco-friendly approach. The morphology, textural features, surface composition and stability of TErGO/Ni₃C-Ni nanocomposite are investigated by various physicochemical characterizations which revealed the uniform dispersion of crystalline metal nanoparticles inside TErGO matrix. The composite has been exhibited a large surface area and pore volume of 121 m² g^-1 and 0.791 cm³  g^-1, respectively. The TErGO/Ni₃C-Ni exhibited remarkable catalytic performance surpassing most metal-based catalysts with various kind of support matrices reported in recent literature. The reduction of Cr(Ⅵ) to Cr(Ⅲ) was achieved within 1 min with an excellent rate constant of 2.74 min^-1 and phenomenally higher specific removal rate (SRR) of 0.29 mg Cr(VI) min^-1.  mg^-1 of TErGO/Ni₃C-Ni. While it also proved an excellent reducing catalyst for organic dyes via NaBH₄ with full reduction achieved within 30 s. Moreover, as prepared nanocatalyst possesses excellent stability and recyclability with easy magnetic separation.

Novel synthesis of a clay supported amorphous aluminum nanocomposite and its application in removal of hexavalent chromium from aqueous solutions

Synthesis and application of bentonite supported amorphous aluminum nanocomposite as promising material for the removal of Cr(vi) from aqueous solutions.

Pure Ni nanocrystallines anchored on rGO present ultrahigh electrocatalytic activity and stability in methanol oxidation

Pure Ni nanoparticles with ultrafine size (2.3 ± 0.4 nm) embedded on rGO present ultrahigh catalytic activity (1600 mA mg^-1), excellent stability (1020 mA mg^-1 retained after 1000 cycles), and a saturation concentration (4 M) of methanol for methanol oxidation reactions, which is better than that of all previously reported Ni-based catalysts.

N-Doped graphene-supported PdCu nanoalloy as efficient catalyst for reducing Cr(vi) by formic acid

Reducing Cr(vi) to Cr(iii) with formic acid is desirable for environmental protection, but the sluggish kinetics limits its practical application, which currently motivates the intensive study of efficient catalysts for this redox reaction. Here bimetallic PdCu nanoalloy (∼5 nm in size) supported by N-doped graphene was synthesized through a one-pot hydrothermal process. The catalytic activity of PdCu nanoalloy highly depends on the Pd/Cu atomic ratio and N-doped graphene support. The obtained Pd₆Cu₄/NG shows superior catalysis towards the Cr(vi) reduction by formic acid with a high kinetic constant (k_n = 23.2 min^-1 mg^-1) and a low activation energy (E_a = 34.9 kJ mol^-1). Active H atoms were found to be the exact reductant for the Cr(vi) reduction, quite different from the reported H₂-reduction route. The enhanced catalysis originates from the electronic and geometric modification of active Pd after formation of PdCu alloy. Electron transfer from Cu to Pd enhances the electron density of Pd atoms, which favors the adsorption of the bridging formate intermediate and subsequent generation of active H atoms over PdCu/NG. The catalyst can be recycled five times without obvious loss of activity. Our work provides an example to explore the alloying effect on the catalytic behavior of PdCu alloy, which may shed light on developing other advanced nanoalloys for Cr(vi) reduction.

Ni nanoparticles on RGO as reusable heterogeneous catalyst: effect of Ni particle size and intermediate composite structures in C-S cross-coupling reaction

The present work demonstrates the C–S cross-coupling reaction between aryl halides and thiols using nickel nanoparticles (Ni NPs) supported on reduced graphene oxide (Ni/RGO) as a heterogeneous catalyst. It is observed that the uniformly dispersed Ni NPs supported on RGO could exhibit excellent catalytic activity in C–S cross-coupling reactions and the catalytic application is generalized with diverse coupling partners. Although the electron-rich planar RGO surface helps in stabilizing the agglomeration-free Ni NPs, the catalytic process is found to occur involving Ni(II) species and the recovered catalyst containing both Ni(0)/Ni(II) species is equally efficient in recycle runs. A correlation of loading of Ni species, size of NPs and the intermediate Ni-related heterostructures formed during the catalytic process has been established for the first time, and found to be best in the C–S cross-coupling reaction for Ni(0) and Ni(II) NPs of the average sizes 11–12 nm and 4 nm, respectively.

Interfacial Growth of TiO2-rGO Composite by Pickering Emulsion for Photocatalytic Degradation

A 2D sandwich-like TiO₂-rGO composite was fabricated by the Pickering emulsion approach to improve the photocatalytic efficiency. Through an in situ growth of antase-TiO₂ nanoparticles on the interface of O/W type GO Pickering emulsion, TiO₂ nanoparticles were closely and densely packed on the surface of well-exfoliated rGO sheets; meanwhile, many mesoporous voids acting as the adsorption chamber and microreactor were produced. Evaluated by methylene blue (MB) degradation, its photocatalytic activity was prominent compared with the common TiO₂-based photocatalyst, with the rate constants 5 and 3.1 times higher under visible light and xenon lamp, respectively. When we applied it in the photocatalytic degradation of tetracycline hydrochloride (TCH, such as 10 ppm) under the visible light without adding any oxidants, the total removal efficiency was as high as 94% after 40 min. The mechanism of this good photocatalytic efficiency was illustrated by the scavenger trapping tests, which showed that this unique structure of TiO₂-rGO composite induced by the Pickering emulsion can significantly enhance the light absorption ability, accelerate the separation rate of electron-hole pairs, increase the adsorption capacity of organic pollutants, and hence improve the photocatalytic efficiency.