Gold nanoparticle and graphene oxide incorporated strontium crosslinked alginate/carboxymethyl cellulose composites for o-nitroaniline reduction and Suzuki-Miyaura cross-coupling reactions

Remediation of soil contaminated with PAHs and γ-HCH using Fenton oxidation activated by carboxymethyl cellulose-modified iron oxide-biochar

The remediation of soil contaminated with hydrophobic organic pollutants has attracted great public concern. In the present study, a novel catalyst using biochar supported ferro ferric oxide modified by carboxymethyl cellulose (CMC-Fe₃O₄/BC) was developed to activate the Fenton reaction for hazardous hydrophobic organic pollutants, and the degradation mechanisms were analyzed in terms of free radicals, electron transfer pathways and degradation intermediates. The results showed that the CMC-Fe₃O₄/BC-activated H₂O₂ system degraded nearly 100% of pyrene in the aqueous system after a 1440-min reaction. The catalyst was also applied to remediate industrial field soil contaminated with PAHs and γ-HCH. The removal rate of the total pollutants reached 61.1% after a 10-day reaction, which was higher than that of Fe₃O₄/BC without modification. CMC enabled the Fe₃O₄ particles to more equably distribute on the BC surface, further effectively activating H₂O₂ to generate more ⋅OH and forming different degradation products compared to the Fe₃O₄/BC. Additionally, the CMC-Fe₃O₄/BC-activated H₂O₂ system obviously enhanced electron transfer on the BC surface. Thus, the PAHs and γ-HCH could be degraded via electron transfer pathways.

Reductive Oligomerization of Nitroaniline Catalyzed by Fe3O4 Spheres Decorated with Group 11 Metal Nanoparticles

The present work demonstrates a simple and sustainable method for forming azo oligomers from low-value compounds such as nitroaniline. The reductive oligomerization of 4-nitroaniline was achieved via azo bonding using nanometric Fe₃O₄ spheres doped with metallic nanoparticles (Cu NPs, Ag NPs, and Au NPs), which were characterized by different analytical methods. The magnetic saturation (M _s) of the samples showed that they are magnetically recoverable from aqueous environments. The effective reduction of nitroaniline followed pseudo-first-order kinetics, reaching a maximum conversion of about 97%. Fe₃O₄-Au is the best catalyst, its a reaction rate (k _Fe3O4-Au = 0.416 mM L^-1 min^-1) is about 20 times higher than that of bare Fe₃O₄ (k _Fe3O4 = 0.018 mM L^-1 min^-1). The formation of the two main products was determined by high-performance liquid chromatography-mass spectrometry (HPLC-MS), evidencing the effective oligomerization of NA through N = N azo linkage. It is consistent with the total carbon balance and the structural analysis by density functional theory (DFT)-based total energy. The first product, a six-unit azo oligomer, was formed at the beginning of the reaction through a shorter, two-unit molecule. The nitroaniline reduction is controllable and thermodynamically viable, as shown in the computational studies.

Strategies adopted for the preparation of sodium alginate–based nanocomposites and their role as catalytic, antibacterial, and antifungal agents

Alginate extracted from the marine brown algae is a massively utilized biopolymer in multiple fields such as microreactors for the fabrication of metal nanoparticles along with other polymeric and nonpolymeric materials to enhance their mechanical strength. These sodium alginate (Na-Alg)-based fabricated nanocomposites find applications in the field of catalysis and biological treatment as antibacterial/antifungal agent due to the synergistic properties of Na-Alg and fabricated metal nanoparticles (NPs). Na-Alg offers mechanical strength and nanoparticles provide high reactivity due to their small size. Sodium alginate exhibits hydroxyl and carboxylate functional groups that can easily interact with the metal nanoparticles to form composite particles. The research on the preparation of Na-Alg–based nanoparticles and nanoaggregates have been started recently but developed quickly due to their extensive applications in different fields. This review article encircles different methods of preparation of sodium alginate–based metal nanocomposites; analytical techniques reported to monitor the formation of these nanocomposites and used to characterize these nanocomposites as well as applications of these nanocomposites as catalyst, antibacterial, and antifungal agent.

Single-ion chelation strategy for synthesis of monodisperse Pd nanoparticles anchored in MOF-808 for highly efficient hydrogenation and cascade reactions

Ultrafine Pd nanoparticles are prepared using a single-ion precursor on a MOF-808 carrier. The ligand 2,3-pyrazinedicarboxylic acid (Pza) is dispersed in porous MOF-808 via grafting on formic acid sites, and thus Pd²⁺ ions are chelated by Pza to form a new single-ion precursor Pd@MOF-808-Pza. Then a Pd-nano@MOF-808-Pza catalyst is prepared by direct reduction of this precursor using NaBH₄. Material characterization reveals the homogeneous dispersion of 3-6 nm Pd nanoparticles within the MOF-808 matrix. Pd-nano@MOF-808-Pza exhibits excellent catalytic activity in the hydrogenation of unsaturated nitrogen-containing compounds, and other typical reactions, such as the Knoevenagel condensation, Suzuki/Heck cross-coupling, and hydrogen tandem reactions. In addition, density functional theory (DFT) calculations are carried out to elucidate the chelation of Pd²⁺ ions by Pza on MOF-808 and propose mechanisms of hydrogenation reactions. This work provides an effective reduction catalyst, and more importantly, a single-ion chelation strategy for design and synthesis of metal supported catalysts.

Nanoarchitectured Cu based catalysts supported on alginate/glycyl leucine hybrid beads for tainted water treatment

Water pollution reached worrying point due to different dye pollutants which demands an instant solution. One of the best ways to manage water pollutants is their reduction and decolorization to less-toxic and useful compounds. However, reduction process requires an effective, stable, and recyclable catalyst to reduce such pollutants more effectively. Metal nanoparticles (M⁰) are highly effective catalysts but separation of nanoparticles after reaction is difficult and requires a high-speed centrifugation. If loaded on polymer-beads, they can be easily separated from the reaction-mixture. Hearin, alginate/glycyl leucine (AGL) hybrid-beads were prepared, and copper nanoparticles (Cu⁰) were grown on it by simple process. M⁰/AGL bead catalysts were tested toward reducing various toxic compounds. Among all developed composite-beads, the catalytic performance of Cu⁰/AGL was highest in terms of reduction kinetics. After initial screening for different pollutants, Cu⁰/AGL was much more effective for MO reduction, thus, all optimized different parameters i.e., catalyst dosage, stability, amount of reducing-agent and recyclability were experimentally determined. The Cu⁰/AGL showed high-rate constants (k_app) of 0.7566 and 2.9506 min^-1 depending on beads content. The reusability of the Cu⁰/AGL catalysts up to the 7^th cycle has been checked. With the use of AGL as support for the Cu nanoparticles, not only the catalytic activity was retained for longer times during reusability, but it helped in their easy separation.

Advances in Graphene/Inorganic Nanoparticle Composites for Catalytic Applications

Graphene-based nanocomposites with inorganic (metal and metal oxide) nanoparticles leads to materials with high catalytic activity for a variety of chemical transformations. Graphene and its derivatives such as graphene oxide, highly reduced graphene oxide, or nitrogen-doped graphene are excellent support materials due to their high surface area, their extended π-system, and variable functionalities for effective chemical interactions to fabricate nanocomposites. The ability to fine-tune the surface composition for desired functionalities enhances the versatility of graphene-based nanocomposites in catalysis. This review summarizes the preparation of graphene/inorganic NPs based nanocomposites and their use in catalytic applications. We discuss the large-scale synthesis of graphene-based nanomaterials. We have also highlighted the interfacial electronic communication between graphene/inorganic nanoparticles and other factors resulting in increased catalytic efficiencies.

Facile d-band tailoring in Sub-10 nm Pd cubes by in-situ grafting on nitrogen-doped graphene for highly efficient organic transformations

We demonstrate for the first time the in-situ synthesis of Pd nanocubes (PdNC) on nitrogen-doped reduced graphene oxide (NRGO) for facile organic transformations wherein the cubic morphology of Pd can only be realized by precision-controlled acid additions in the tune of 0.02 pH variations in the reaction medium. Due to the intimate contact arising from atom-by-atom addition of Pd on NRGO, the composite has exhibited a pronounced catalyst to support charge transfer effect, shift in the d-band center, and lowering of charge-transfer resistance when compared with PdNC-NRGO ex-situ composites prepared by mixing of the preformed components of PdNC and NRGO or PdNCs alone. The activities of these catalysts were tested for the Suzuki coupling and nitroarene reduction reactions using water as an industry-friendly solvent. In both, the in-situ deposited sample exhibited substantially higher catalytic activity as well as stability when compared with an ex-situ sample or pure PdNCs. We show that a very high turnover frequency of ~31300 h^-1 and ~900 h^-1 are achievable by using the in-situ deposited PdNC-NRGO composite for Suzuki coupling reactions and nitroarene reduction respectively, better than the state-of-the-art catalysts developed recently, in addition to high recyclability.

Strong interaction between Au nanoparticles and porous polyurethane sponge enables efficient environmental catalysis with high reusability

A novel and recoverable platform of polyurethane (PU) sponge-supported Au nanoparticle catalyst was obtained by a water-based in-situ preparation process. The structure, chemical, and morphology properties of this platform were characterized by XRD, TGA, SEM, FT-IR, and XPS. The Au/PU sponge platform exhibited excellent catalytic performances in catalytic reductions of p-nitrophenol and o-nitroaniline at room temperature, and both catalytic reactions could be completed within 4.5 and 1.5 min, respectively. Furthermore, the strong interaction between Au nanoparticles and the PU sponge enabled the catalyst system to maintain a high catalytic efficiency after 5 recycling times, since the PU sponge reduced the trend of leaching and aggregation of Au nanoparticles. The unique nature of Au nanoparticles and the porous PU sponge along with their strong interaction resulted in a highly efficient, recoverable, and cost-effective multifunctional catalyst. The AuNP/Sponge nanocatalyst platform has great potential for wide environmental and other catalytic applications.

Carboxymethyl cellulose nanocomposite beads as super-efficient catalyst for the reduction of organic and inorganic pollutants

Carboxymethyl cellulose/copper oxide-nickel oxide (CMC/CuO-NiO) nanocomposite beads were prepared by facile, simple and environmentally friendly method. Initially, CuO-NiO was prepared and applied for the catalytic reduction of 4-nitrophenol (4-NP). The results showed that CuO-NiO demonstrate high catalytic activity toward the reduction of 4-NP to 4-aminophenol (4-AP) with a rate constant of 2.97 × 10^-2 s^-1. Further, CuO-NiO were well-dispersed in the polymeric matrix of carboxymethyl cellulose to prepare CMC/CuO-NiO beads. CMC/CuO-NiO nanocomposite beads were also applied to catalyze the reduction of potassium ferrocyanide (K₃Fe (CN)₆), 4-NP, Congo red (CR) and Eosin yellow (EY) in the presence of sodium borohydride. Experimental data indicated that CMC/CuO-NiO nanocomposite has higher catalytic activity and high rate constant compared to CuO-NiO. The rate constant found to be 6.88 × 10^-2, 6.27 × 10^-2, 1.89 × 10^-2 and 2.43 × 10^-2 for K₃Fe(CN)₆, 4-NP, CR and EY, respectively, using 5 mg CMC/CuO-NiO beads. FE-SEM, EDX, FTER, XRD and XPS were used to characterize the nanocomposites. CMC/CuO-NiO beads catalytically reduced up to 95-99% of K₃Fe(CN)₆, 4-NP, CR and EY within 40, 60, 120 and 120 s. CMC/CuO-NiO beads were found more selective for the reduction of 4-NP. The catalytic reduction performance of CMC/CuO-NiO beads was optimized by studying the influence of different parameters on the catalytic reduction of 4-NP. Hence, the effective and super catalytic performance toward the reduction of different organic and inorganic pollutants makes CMC/CuO-NiO beads a smart material and suitable for numerous scientific and industrial applications and may be used as an alternative to high-cost commercial catalysts.

Role of the Support in Gold-Containing Nanoparticles as Heterogeneous Catalysts

In this review, we discuss selected examples from recent literature on the role of the support on directing the nanostructures of Au-based monometallic and bimetallic nanoparticles. The role of support is then discussed in relation to the catalytic properties of Au-based monometallic and bimetallic nanoparticles using different gas phase and liquid phase reactions. The reactions discussed include CO oxidation, aerobic oxidation of monohydric and polyhydric alcohols, selective hydrogenation of alkynes, hydrogenation of nitroaromatics, CO₂ hydrogenation, C–C coupling, and methane oxidation. Only studies where the role of support has been explicitly studied in detail have been selected for discussion. However, the role of support is also examined using examples of reactions involving unsupported metal nanoparticles (i.e., colloidal nanoparticles). It is clear that the support functionality can play a crucial role in tuning the catalytic activity that is observed and that advanced theory and characterization add greatly to our understanding of these fascinating catalysts.

Recyclable Au/SiO2-Shell/Fe3O4-Core Catalyst for the Reduction of Nitro Aromatic Compounds in Aqueous Solution

Highly stable gold nanoparticles immobilized on the surface of amine-functionalized nanocomposite microspheres possessing a magnetite (Fe₃O₄) nanoparticle core and a silica (SiO₂) shell (Au/SiO₂-shell/Fe₃O₄-core) were prepared. These gold nanocomposite catalysts were tested for 4-nitrophenol (4-NP) and 2-nitroaniline (2-NA) reduction in aqueous solution in the temperature range 293-323 K and in the presence of aqueous NaBH₄ reducing agent. The magnetically recyclable gold catalyst showed high stability (∼3 months), efficient recyclability (up to 10 cycles), and high activity (∼100% conversion within 225 s, ∼700 ppm 4-NP or 2-NA). The pseudo-first-order apparent reaction rate constants (k) of 4-NP and 2-NA reduction were 7.5 × 10^-3 and 4.1 × 10^-3 s^-1, respectively, and with an apparent catalytic activity of 4.48 × 10^-8 kmol/(m³ s).

Insightful understanding of the correlations of the microstructure and catalytic performances of Pd@chitosan membrane catalysts studied by positron annihilation spectroscopy

In this study, the catalytic performances of palladium supported on chitosan (Pd@CS) membrane heterogeneous catalysts have been studied from the aspects of free volume by positron annihilation lifetime spectroscopy (PALS). The results showed that the variation in free volume hole size of the Pd@CS membrane catalyst was closely associated with microstructure evolutions, such as increase of Pd content, valence transition of Pd by reduction treatment, solvent swelling, physical aging during catalyst recycling, and so on. The PALS results showed that both the mean free volume hole size of the Pd⁰@CS membrane in the dry or swollen state (analyzed by the LT program) and its distribution (analyzed by the MELT program) are smaller than the molecule size of the reactants and products in the catalysis reaction. However, the results showed that the Pd⁰@CS membrane catalyst has excellent catalytic activity for the Heck coupling reaction of all the reactants with different molecule size. It was revealed that the molecule transport channels of the Pd⁰@CS membrane catalyst in the reaction at high temperature was through a number of instantaneously connected free volume holes rather than a single free volume hole. This hypothesis was powerfully supported by the catalytic activity assessment results of the CS layer sealed Pd⁰@CS membrane catalyst. Meanwhile, it was confirmed that the leaching of Pd⁰ nanoparticles of the reused Pd⁰@CS membrane catalyst during the recycling process was also through such instantaneously connected free volume holes.

A number of instantaneously connected free volume holes act as mass transport channels of the Pd⁰@CS membrane catalyst in reactions.