Covalently functionalized carbon nanotube supported Pd nanoparticles for catalytic reduction of 4-nitrophenol

Nitrophenol Reduction with Silver Oxide Nanostructures as a Sustainable Approach to Environmental Remediation

We propose silver oxide as a cost-effective and sustainable alternative to noble metals for the catalytic reduction of nitroaromatics. In the present investigation, we adopt a facile and green synthetic route for the synthesis of silver oxide nanostructures. The prepared nanostructures were found to crystallize in the cuprite phase and exhibit absorbance across the entire visible range of the electromagnetic spectrum. The catalytic potential of the silver oxide was evaluated by following the kinetics of nitrophenol reduction under ambient conditions and is observed to follow pseudo-first order kinetics with the apparent rate constantk a p p = 4 . 24 × 10 - 3 ${{k}_{app}=4.24\ \times {10}^{-3}}$ s-1 at minimum concentration of the catalyst. We attribute the observed catalytic activity to the freshly generated catalytic surface featuring a partially reduced form of silver oxide during reaction. The findings highlight the efficacy of silver oxide in mitigating the environmental pollution originating from the recalcitrant nitroarenes.

Catalytic Reduction of p-Nitrophenol on MnO2/Zeolite -13X Prepared with Lawsonia inermis Extract as a Stabilizing and Capping Agent

p-nitrophenol (pNP) is a highly toxic organic compound and is considered carcinogenic and mutagenic. It is a very stable compound with high resistance to chemical or biological degradation. As a result, the elimination of this pollutant has been very challenging for many researchers. Catalytic reduction is one of the most promising techniques, if a suitable catalyst is developed. Thus, this work aims to prepare an eco-friendly catalyst via a simple and low-cost route and apply it for the conversion of the toxic p-nitrophenol (pNP) into a non-toxic p-aminophenol (pAP) that is widely used in industry. Manganese oxide was prepared in an environmentally friendly manner with the aid of Lawsonia inermis (henna) extract as a stabilizing and capping agent and loaded on the surface of 13X molecular sieve zeolite. The UV-Vis spectrum, EDS, and XRD patterns confirmed the formation of the pure MnO₂ loaded on the zeolite crystalline network. The TGA analysis showed that the samples prepared by loading MnO₂ on zeolite (Mn2Z, Mn3Z, and Mn4Z) lost more mass than pure MnO₂ (Mn) or zeolite (Z), which is mainly moisture adsorbed on the surface. This indicates a better dispersion of MnO₂ on the surface of zeolite compared to pure MnO₂, and thus a higher number of active adsorption sites. SEM images and EDS confirmed the dispersion of the MnO₂ on the surface of the zeolite. Results showed a very fast reduction rate, following the order Mn2Z > Mn3Z > Mn4Z > Mn > Z. With sample Mn2Z, 96% reduction of pNP was achieved in 9 min and 100% in 30 min. For Mn3Z, Mn4Z, and Mn, 98% reduction was achieved in 20 min and 100% in 30 min. Zeolite was the slowest, with only a 40% reduction in 30 min. Increasing the amount of zeolite in the synthesis mixture resulted in lower reduction efficiency. The kinetic study indicated that the reduction of p-nitrophenol on the surface of the prepared nanocomposite follows the pseudo-first-order model. The results show that the proposed nanocomposite is very effective and very promising to be commercially applied in water treatment, due to its low cost, simple synthesis procedure, and reusability.

In Situ Implantation of Bi2S3 Nanorods into Porous Quasi-Bi-MOF Architectures: Enabling Synergistic Dissociation of Borohydride for an Efficient and Fast Catalytic Reduction of 4-Nitrophenol

Catalytic hydrogenation reduction based on sodium borohydride (NaBH₄) has gained attention as an appealing "one-stone-two-birds" approach for the simultaneous elimination of nitroaromatic pollutants and the production of high-value aminoaromatics under mild conditions. However, the slow kinetics of NaBH₄ dissociation on the surface of catalysts restrict the catalytic hydrogenation reduction efficiency. Herein, we report an intelligent localized sulfidation strategy for an in situ implantation of Bi₂S₃ nanorods within quasi-Bi-MOF architectures (Bi₂S₃@quasi-Bi-MOF) by fine-tuning the pyrolysis temperature. In this novel Bi₂S₃@quasi-Bi-MOF, the porous quasi-Bi-MOF enables efficient adsorption of BH₄^- and 4-nitrophenol (4-NP), while Bi₂S₃ facilitates the BH₄^- dissociation to form H_ads* species adsorbed on the catalyst surface. Benefiting from the synergistic structure, Bi₂S₃@quasi-Bi-MOF exhibits excellent performance for the catalytic reduction of 4-NP, delivering a high turnover frequency (TOF) of 1.67 × 10^-4 mmol mg^-1 min^-1 and an extremely high normalized rate constant (k_nor) of 435298 s^-1 g^-1. The kinetic analysis and electrochemical tests indicate that this catalytic hydrogenation reduction follows the Langmuir-Hinshelwood mechanism. This study enriches the synthetic strategy of MOF-based derivatives and offers a new catalytic platform for hydrogenation reduction reactions.

Synthesis of stack plate covalent organic framework nanotubes using a self-assembled acid as a soft template

COF-LZU1 with nanotube-like morphology has been synthesized with high crystallinity and pore volume in the presence of trimesic acid as a template. The as-synthesized COF nanotubes consist of a stack of plates with a diameter of about 100 nm with a hollow channel inside of about 20 nm.

Hierarchical-Structured Pd Nanoclusters Catalysts x-PdNCs/CoAl(O)/rGO-T by the Captopril-Capped Pd Cluster Precursor Method for the Highly Efficient 4-Nitrophenol Reduction

Water-soluble captopril-capped atomically precise Pd nanoclusters (Pd₁₇Capt₈ NCs: 1.3 ± 0.5 nm) produced by a simple chemical reduction were supported on preprepared hybrid Co₃Al-layered double hydroxide/reduced graphene oxide (Co₃Al-LDH/rGO) by a pH-adjusted electrostatic adsorption strategy followed by proper calcinations, giving a series of novel catalysts x-PdNCs/CoAl(O)/rGO-T (x (Pd loading) = 0.09, 0.17, 0.43 wt % (ICP), T = 230, 250, 280, 300, 320 °C). The characterization results show that the as-obtained catalysts possess the hierarchical nanosheet array morphology. Pd NCs with a size of ∼1.3 to 1.8 nm are highly distributed at the edge sites of the CoAl(O) nanosheets. All of the x-PdNCs/CoAl(O)/rGO-T catalysts show superior catalytic efficiency for the conversion of 4-nitrophenol to 4-aminophenol, particularly 0.17-PdNCs/CoAl(O)/rGO-300 possesses the highest performance with a turnover frequency (TOF) of 30 042 h^-1, which is the highest among the reported Pd-based catalysts so far. The superior activity of 0.17-PdNCs/CoAl(O)/rGO-300 can be owing to ultrafine Pd NCs with a clean surface, the strongest PdNCs-Co²⁺-OH(LDH)-rGO three-phase synergy, and the much improved adsorption of the substrate via π-π stacking upon nanosheet array morphology. Meanwhile, 0.17-PdNCs/CoAl(O)/rGO-300 exhibits excellent catalytic activities for various nitroarenes and anionic azo dyes as well as good reusability with the complete reduction of 4-nitrophenol (4-NP) within 90 s after 10 successive runs. The present work provides not only a simple and convenient strategy for the synthesis of clean, efficient, and environmentally friendly supported metal nanocluster catalysts but also a new idea for the efficient catalytic degradation of environmental pollutants.

Cofactors-like peptide self-assembly exhibiting the enhanced catalytic activity in the peptide-metal nanocatalysts

The peptide self-assembly would be expected to be as the assistance of metallic nanocatalysts to promote the catalytic reaction, attracting limited attention, but being highly anticipated. Herein, we proposed and verified an alternative strategy for enhancing the catalytic activity of the 4-nitrophenol reduction as a model reaction, by optimizing and constructing "cofactors" inspired amyloid peptide self-assembly applied in the peptide-metal nanocatalysts as the template due to the potential superiority of substrate binding. Amyloid peptide self-assembled membrane exhibited better enhanced catalytic activity, compared to peptide nanofibers as the template in the peptide-gold nanocatalysts. The optimized amyloid peptide was designated by molecular dynamic simulation to display the relative strongest interaction with specific substrate and the relative good template effect on the enhanced catalytic activity was also proved accordingly. This work may shed light on the future design and construction of novel enzyme mimics with dramatic enhanced catalytic activity by peptide assembly-metal nanocatalysts.

A catalyzed method to remove polychlorinated biphenyls from contaminated transformer oil

The disposal of polychlorinated biphenyls (PCBs) as persistent organic pollutants from the environment has been normally performed by isolation from soil or water because of their biological activity and toxic potential. In the present investigation, catalytic hydrodehalogenation was used to detoxify PCBs-contaminated transformer oil. All reactions were directed on an oil containing 11.09 wt% of PCBs utilizing palladium supported on multi-walled carbon nanotubes (Pd/MWCNTs). The amount of hexa-chlorine homologues reduced considerably from 5.07% to less than 800 ppm utilizing HDC at the atmosphere of argon. Moreover, the amounts of long half-lives and bioaccumulative congener of PCB 153 decreased considerably from 3.2% to less than 200 ppm. Besides, the quantity of some environmental pollutants like PCB 105 as a mono-ortho-substituted congener decreased considerably. The significant effects of reaction time, reaction temperature, and catalyst concentration on the efficiency were confirmed and modeled through Box-Behnken design. The optimal reaction condition with an efficiency of 96.67% was 70°C, with catalyst loading of 8 wt% and reaction time of 3.23 h. Furthermore, the quantity of turnover frequency of Pd/MWCNTs showed that it has more activity than palladium-carbon active supported in the ambient pressure without utilizing hydrogen gas in transformer oil complex. The study of the kinetic model revealed that the required activation energy (of 12.99 kJ/mol) to remove PCBs from transformer oil utilizing the present catalyst was lower than other catalyzed hydrodechlorination methods.

Highly efficient catalytic reduction of 4-nitrophenol and organic dyes by ultrafine palladium nanoparticles anchored on CeO2 nanorods

Uniformly dispersed Pd nanoparticles on certain supports exhibit exceptional catalytic performance toward various environmental applications. In this work, ultrafine Pd nanoparticles anchored on CeO₂ nanorods were synthesized via an absorption-in situ reduction method. The activity of the CeO₂/Pd nanocomposites was systematically investigated toward reduction of 4-nitrophenol (4-NP) and organic dyes including methyl blue, rhodamine B, methyl orange, and Congo red. The results indicated that the CeO₂/Pd nanocomposites with different weight ratios of Pd nanoparticles (10.23 wt%, 11.01 wt%, and 14.27 wt%) can almost completely reduce 4-NP with a rate constant of 3.31×10^-1, 3.22×10^-1, and 2.23×10^-1 min^-1. Besides, the 10.23 wt% CeO₂/Pd nanocomposites exhibit remarkable enhanced catalytic activity toward reduction of organic dyes. The catalysts display ideal stability after being used for three times for the reduction of 4-NP. We believe that our strategy demonstrated here offers insights into the design and fabrication of novel Pd-based nanocomposites for various heterogeneous catalysis applications.

Synthesis of disordered mesoporous silica loaded with ultrasmall-sized CuO nanoparticles based on an alkali-free strategy and its excellent catalytic performance in the reduction of organic dye

In this paper, disordered mesoporous silica loaded with ultrasmall-sized and highly dispersed CuO nanoparticles was obtained by an alkali-free strategy. Pre-prepared copper bromoacetate (CuBA) and (3-aminopropyl)triethoxysilane (APTES) were selected as reactants, which can be covalently connected with each other for the formation of functional hybrid precursors. Simultaneously, the protonated amino group with the ability to promote the hydrolysis of silane was generated, avoiding any additional catalyst. The covalent introduction of copper salt by chemical bonding promised the molecular-level dispersion of copper ions, favouring the in situ generation of ultrasmall-sized and highly dispersed CuO nanoparticles in the silica matrix. The average diameter of this obtained composited silica material is around 700 nm, and CuO nanoparticles with an average diameter of ∼3 nm were uniformly dispersed in the silica matrix. Typically, disordered mesopores were obtained under the thermolysis of organic chains in the hybrid silica matrix; the BET surface area is 77 m² g⁻¹ and the pore diameter is about 2.5 nm. The catalytic property was investigated and the results show that this obtained CuO@mSiO₂ material has good catalytic performance in the reduction of organic dye with NaBH₄ as the reducing agent.

Mesoporous silica loaded with ultrasmall sized and highly dispersed CuO nanoparticles was synthesized based on an alkali-free strategy. The obtained silica material has excellent catalytic performance on reduction MB dye in the presence of NaBH₄ as reductant.

Carbon nanotubes obtained from commercial resins with different treatment temperatures

Carbon nanotubes were prepared with commercial resin by a simple method to explore the effects of different calcination temperatures.

Modification of structured bio‑carbon derived from spongin-based scaffolds with nickel compounds to produce a functional catalyst for reduction and oxidation reactions: Potential for use in environmental protection

Three different 3D fibrous-like NiO/Ni(OH)₂/Ni‑carbonized spongin-based materials were prepared via a simple sorption-reduction method. Depending on the support used, the catalysts were composed of carbon, nickel oxide, nickel hydroxide and zero-valent nickel, with the surface content of the nickel-containing phase in the range 15.2-26.0 wt%. Catalytic studies showed promising activity in the oxidation of phenolic compounds in water and in the reduction of 4-nitrophenol. The oxidation efficiency depends on the substrate used and ranges from 80% for phenol at pH 2 to 99% for 4-chlorophenoxyacetic acid (4-CPA) and methylchlorophenoxypropionic acid (MCPP). In the reduction reaction, all catalysts exhibited superior activity, with rate constants in the range 0.648-1.022 min^-1. The work also includes a detailed investigation of reusability and kinetic studies.

Size-Dependent Catalytic Activity of PVA-Stabilized Palladium Nanoparticles in p-Nitrophenol Reduction: Using a Thermoresponsive Nanoreactor

Palladium nanoparticles (Pd NPs) of various average global diameters (2.1-7.1 nm) encapsulated with hydrophilic polymer polyvinyl alcohol (PVA) have been synthesized and used as catalysts for sodium borohydride assisted reduction of p-nitrophenol to p-aminophenol. The synthesized catalysts exhibit excellent and typical size-dependent catalytic activity in the green protocol. UV-visible absorption spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were employed to characterize the prepared Pd NPs. The kinetics of this reaction was easily monitored by a UV-visible absorption spectrophotometer. The mechanism of the reaction is explained by the Langmuir-Hinshelwood model. The catalytic performance increases with decreasing size of the synthesized nanoparticles. The apparent rate constants (k app × 103/s-1) of the catalytic reduction in the presence of Pd NPs of average diameters of 2.1, 3.35, 6.2, and 7.1 nm are determined as 8.57, 7.67, 6.16, and 5.04, respectively, at 298 K by using 2.91 mol % palladium nanocatalyst in each case. Moreover, the estimated activation energy of 22.2 kJ mol-1 obtained for Pd NPs with the smallest average diameter of 2.1 nm is very low as reported in the literature for the reduction. The influences of catalyst dose and concentration of p-nitrophenol on catalytic reduction are fully investigated. The catalyst with the largest diameter shows a temperature-sensitive property that might be due to the presence of a very low amount of rapped PVA used as stabilizer during the fabrication process. Thus, the synthetic protocol provides a unique fabrication process of a catalytically active thermoresponsive nanoreactor consisting of Pd NPs encapsulated into a PVA stabilizing agent.

A novel Au/electroactive poly(amic acid) composite as an effective catalyst for p-nitrophenol reduction

A Au/electroactive poly(amic acid) (Au/EPAA) composite was synthesized and characterized, and its catalytic ability was evaluated. EPAA was synthesized via oxidative coupling polymerization and Au nanoparticles were anchored to the amino and carboxyl groups. The Au/EPAA composite was characterized via X-ray diffraction analysis, X-ray photoelectron spectroscopy, and scanning electron microscopy, which confirmed that the Au nanoparticles were well dispersed on the EPAA surface. p-Nitrophenol was reduced to p-aminophenol within 5 min at room temperature, with a rate constant of 0.84 min⁻¹. Cycling measurements showed that the Au/EPAA composite achieved higher than 92% conversion. The Au/EPAA composite showed excellent performance and stability as a catalyst for the reduction of p-nitrophenol to p-aminophenol.

The Au/EPAA composite demonstrated excellent performance and stability as a catalyst for the reduction of p-nitrophenol to p-aminophenol.

Understanding Hydrodechlorination of Chloromethanes. Past and Future of the Technology

Chloromethanes are a group of volatile organic compounds that are harmful to the environment and human health. Abundant studies have verified that hydrodechlorination might be an effective treatment to remove these chlorinated pollutants. The most outstanding advantages of this technique are the moderate operating conditions used and the possibility of obtaining less hazardous valuable products. This review presents a global analysis of experimental and theoretical studies regarding the hydrodechlorination of chloromethanes. The catalysts used and their synthesis methods are summarized. Their physicochemical properties are analyzed in order to deeply understand their influence on the catalytic performance. Moreover, the main causes of the catalyst deactivation are explained, and prevention and regeneration methods are suggested. The reaction systems used and the effect of the operating conditions on the catalytic activity are also analyzed. Besides, the mechanisms and kinetics of the process at the atomic level are reviewed. Finally, a new perspective for the upgrading of chloromethanes, via hydrodechlorination, to valuable hydrocarbons for industry, such as light olefins, is discussed.

Ru single atoms and nanoparticles on carbon nanotubes as multifunctional catalysts

In the last decade we have witnessed increasing interest in the production of renewable energy and value-added chemicals through sustainable and low-cost technologies where catalysts play a crucial role. Herein, we report the application of a Ru/CNT material containing a mixture of Ru single atoms and Ru nanoparticles as a multifunctional catalyst for both the catalytic reduction of nitroarenes and the electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The catalytic activity of the Ru-CNT material was evaluated in the reduction of 4-nitrophenol (4-NP), 4-nitroaniline (4-NA) and 2-nitrophenol (2-NP) in the presence of sodium borohydride as a reducing agent at room temperature, showing high catalytic activity with normalized rate constants (k_nor) of 19.0 × 10³, 57.7 × 10³ and 16.6 × 10³ min^-1 mmol^-1 respectively. Furthermore, the catalyst could be reused in at least 10 cycles without catalytic activity loss, confirming the high stability and robustness of the material. The Ru/CNT material also showed good ORR electrocatalytic activity in alkaline medium with E_onset of 0.76 V vs. RHE, a diffusion-limited current density of 3.89 mA cm^-2 and ñ_O2 of 3.3. In addition, Ru/CNT was remarkably insensitive to methanol with a current retention of 93% (51% for Pt/C) and competitive electrochemical stability of 80% after 20 000 s. Moreover, Ru/CNT was active for the OER with j_max = 29.5 mA cm^-2 at E = 1.86 V vs. RHE, η₁₀ = 0.50 V and good stability (η₁₀ changed to 0.01 V and j_max only decreased by ≈12% after 500 cycles).

Controlled Synthesis of Palladium Nanocubes as an Efficient Nanocatalyst for Suzuki-Miyaura Cross-Coupling and Reduction of p-Nitrophenol

Anisotropic nanocatalysts have attracted considerable attention in comparison to bulk/nanocatalysts for their enhanced activity and reactivity. The demand toward anisotropic palladium (Pd) nanostructures has increased rapidly in the field of catalysis. Pd is a well-known active catalyst for several carbon-carbon (C-C) cross-coupling reactions; among them, the Suzuki-Miyaura cross-coupling reaction is one of the most versatile and dominant methods for constructing the extraordinarily useful unsymmetrical biaryls and also for hydrogenation of organic contaminants like p-nitrophenol (p-NP). This paper provides a brief explanation about the controlled synthesis, characterization, and catalytic activity of well-defined palladium nanocubes (Pd NCs) prepared by a seed-mediated method. The synthesized monodispersed Pd NCs were characterized by spectroscopic and microscopic tools such as UV-visible, XRD, FESEM, HRTEM, and EDS analyses. Pd NCs proved as an efficient catalyst for Suzuki-Miyaura cross-coupling reactions and p-NP reduction. The catalyst shows enhanced activity, greater stability, and higher selectivity with remarkable recyclability up to 92% for five consecutive cycles. The catalytic performance of the synthesized Pd NCs was also studied in the reduction of the organic contaminant p-NP, which showed an excellent performance screening of 99% conversion in 6 min.

Highly Active Hydrogenation Catalysts Based on Pd Nanoparticles Dispersed along Hierarchical Porous Silica Covered with Polydopamine as Interfacial Glue

New catalysts based on Pd(0) nanoparticles (Pd NPs) on a bimodal porous silica of the UVM-7/polydopamine (PDA) support have been synthesized following two preparative strategies based on the sequential or joint incorporation of two components of the composite (Pd and PDA). We analyzed the role played by the PDA as ‘interfacial glue’ between the silica scaffold and the Pd NPs. The catalysts were tested for the hydrogenation of 4-nitrophenol using (NEt4)BH4 as the hydrogenating agent. In addition to the palladium content, the characterization of the catalysts at the micro and nanoscale has highlighted the importance of different parameters, such as the size and dispersion of the Pd NPs, as well as their accessibility to the substrate (greater or lesser depending on their entrapment level in the PDA) on the catalytic efficiency. Staged sequential synthesis has led to better catalytic results. The most active Pd(0) centers seem to be Pd NPs of less than 1 nm on the PDA surface. The efficiency of the catalysts obtained is superior to that of similar materials without PDA. A comprehensive comparison has been made with other catalysts based on Pd NPs in a wide variety of supports. The TOF values achieved are among the best described in the literature.

Janus coordination polymer derived PdO/ZnO nanoribbons for efficient 4-nitrophenol reduction

Bimetallic coordination polymers–Zn(MAA)₂/Pd(ii) nanoribbons are prepared by employing two terminal units with distinct hard–soft properties of the smallest semi-rigid methacrylate anion to combine with two different metal ions.

Sub-10 nm Ag Nanoparticles/Graphene Oxide: Controllable Synthesis, Size-Dependent and Extremely Ultrahigh Catalytic Activity

While tremendous advancements in Ag nanoparticle (AgNP)-based materials have been made, the development of a facile protocol for preparing sub-10 nm AgNPs with controllable size and ultrahigh performance remains a formidable challenge. It is shown that AgNPs/graphene oxide (AgNPs/GO) bearing 2.5, 4.3, and 6.2 nm AgNPs (2.5-AgNPs/GO, 4.3-AgNPs/GO, and 6.2-AgNPs/GO, respectively) could be fabricated via light-induced synthesis. Their catalytic activity toward 4-nitrophenol (4-NP) reduction, which is a "gold standard" for evaluating the performance of noble metal-based catalysts, is studied. When normalized by mole and area, the activity exhibits an order of 4.3-AgNPs/GO > 6.2-AgNPs/GO > 2.5-AgNPs/GO and 6.2-AgNPs/GO > 4.3-AgNPs/GO > 2.5-AgNPs/GO, respectively. This trend is a result of GO-induced electron concentration reduction with decreasing AgNP size. Significantly, under similar conditions, the activity of 4.3-AgNPs/GO is substantially superior to that of numerous state-of-the-art noble metal-based catalysts. The ultrafine size of the AgNPs and their surface accommodation on the unobstructed 2D GO scaffolds without capping reagents/covers, which make the abundantly exposed catalytically active sites highly accessible to substrate molecules, play an important role in their extremely ultrahigh performance. This work paves a new avenue for high-performance AgNP-based materials, and by taking 4-NP reduction as a proof-of-concept, provides new scientific insights into the rational design of surface-based advanced materials.

Monolithic cellulose supported metal nanoparticles as green flow reactor with high catalytic efficiency

A highly effective, stable and reusable flow microreactor was developed by utilizing the environmentally sustainable porous monolithic cellulose based on a facile temperature induced phase separation (TIPS) method. The obtained microreator could be applied to efficiently and continuously catalysing the reduction reaction of 4-nitrophenol (an important reaction in water treatment) without any post-treatment or regeneration of catalysts. Moreover, the monolith overcame the brittleness of the crystalline cellulose and showed a good mechanical resilience, suggesting a great potential for the practical application in severe environment. Compared with previous reported Pd supported catalytic systems, this microreactor exhibited extremely high catalytic efficiency (turnover frequency, TOF = 4660 h^-1, almost 4 times higher than that of cellulose nanocrystals supported catalyst) and long-term stability. This work provided a new strategy to construct highly effective and reusable metal NPs involved catalytic system by utilizing biodegradable cellulose materials.

Ruthenium Supported on Ionically Cross-linked Chitosan-Carrageenan Hybrid MnFe2O4 Catalysts for 4-Nitrophenol Reduction

Herein, we report a facile procedure to synthesize the hybrid magnetic catalyst (Ru@CS-CR@Mn) using ruthenium (Ru) supported on ionically cross-linked chitosan-carrageenan (CS-CR) and manganese ferrite (MnFe2O4) nanoparticles with excellent catalytic activity. The ionic gelation of CS-CR is acting as a protecting layer to promote the encapsulation of MnFe2O4 and Ru nanoparticles by electrostatic interactions. The presence of an active metal and a CS-CR layer on the as-prepared Ru@CS-CR@Mn catalyst was well determined by a series of physicochemical analyses. Subsequently, the catalytic performances of the Ru@CS-CR@Mn catalysts were further examined in the 4-nitrophenol (4-NP) reduction reaction in the presence of sodium borohydride (reducing agent) at ambient temperature. The Ru@CS-CR@Mn catalyst performed excellent catalytic activity in the 4-NP reduction, with a turnover frequency (TOF) values of 925 h−1 and rate constant (k) of 0.078 s−1. It is worth to mentioning that the Ru@CS-CR@Mn catalyst can be recycled and reused up to at least ten consecutive cycles in the 4-NP reduction with consistency in catalytic performance. The Ru@CS-CR@Mn catalyst is particularly attractive as a catalyst due to its superior catalytic activity and superparamagnetic properties for easy separation. We foresee this catalyst having high potential to be extended in a wide range of chemistry applications.

Ferrocenyl metal–organic framework hollow microspheres for in situ loading palladium nanoparticles as a heterogeneous catalyst

Zn–Fc MOF hollow microspheres were prepared for the in situ reduction of Pd²⁺ into Pd nanoparticles as a highly efficient heterogeneous catalyst.

Self-immobilized Pd nanowires as an excellent platform for a continuous flow reactor: efficiency, stability and regeneration

Despite extensive use of Pd nanocrystals as catalysts, the realization of a Pd-based continuous flow reactor remains a challenge. Difficulties arise due to ill-defined anchoring of the nanocrystals on a substrate and reactivity of the substrate under different reaction conditions. We demonstrate the first metal (Pd) nanowire-based catalytic flow reactor that can be used across different filtration platforms, wherein, reactants flow through a porous network of nanowires (10-1000 nm pore sizes) and the product can be collected as filtrate. Controlling the growth parameters and obtaining high aspect ratio of the nanowires (diameter = ∼13 nm and length > 8000 nm) is necessary for successful fabrication of this flow reactor. The reactor performance is similar to a conventional reactor, but without requiring energy-expensive mechanical stirring. Synchrotron-based EXAFS studies were used to examine the catalyst microstructure and Operando FT-IR spectroscopic studies were used to devise a regenerative strategy. We show that after prolonged use, the catalyst performance can be regenerated up to 99% by a simple wash-off process without disturbing the catalyst bed. Thus, collection, regeneration and redispersion processes of the catalyst in conventional industrial reactors can be avoided. Another important advantage is avoiding specific catalyst-anchoring substrates, which are not only expensive, but also non-universal in nature.

Photoinduced in Situ Deposition of Uniform and Well-Dispersed PtO2 Nanoparticles on ZnO Nanorods for Efficient Catalytic Reduction of 4-Nitrophenol

Based on the photochemical property of semiconductors, a light irradiation-assisted strategy has been designed using one-dimensional ZnO nanorods as carriers to synthesize the rod-type PtO₂/ZnO catalyst with a well-defined structure. The high crystallinity and uniform crystal structure of the ZnO matrix conduct the in situ deposition of PtO₂ nanoparticles with 1.1-2.1 nm, which are evenly and densely anchored on the surface. Those small-sized and well-dispersed PtO₂ nanoparticles endow the PtO₂/ZnO catalyst a superior catalytic performance for the reduction of 4-nitrophenol to 4-aminophenol, which can convert all the substrates within 6.25 min. It is demonstrated that the catalytic activity of the PtO₂/ZnO catalyst is 2.3 times as high as that of the sample obtained by traditional wet-oxidation method under the same reaction conditions. Moreover, the light-irradiation time has been found to greatly affect the structure and activity of PtO₂/ZnO catalysts, and the product with 30 min exhibits the best catalytic performance in this work, as well as the good stability for ten runs. In terms of the photoexcited process of ZnO and reactive species-trapped experiments, the formation mechanism of PtO₂/ZnO catalysts has been explored in detail, which will probably stimulate the design and study of other metal-supported catalysts.

Facile Fabrication of Highly Active Magnetic Aminoclay Supported Palladium Nanoparticles for the Room Temperature Catalytic Reduction of Nitrophenol and Nitroanilines

Magnetically recyclable nanocatalysts with excellent performance are urgent need in heterogeneous catalysis, due to their magnetic nature, which allows for convenient and efficient separation with the help of an external magnetic field. In this research, we developed a simple and rapid method to fabricate a magnetic aminoclay (AC) based an AC@Fe₃O₄@Pd nanocatalyst by depositing palladium nanoparticles (Pd NPs) on the surface of the magnetic aminoclay nanocomposite. The microstructure and the magnetic properties of as-prepared AC@Fe₃O₄@Pd were tested using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and vibrating sample magnetometry (VSM) analyses. The resultant AC@Fe₃O₄@Pd nanocatalyst with the magnetic Fe-based inner shell, catalytically activate the outer noble metal shell, which when combined with ultrafine Pd NPs, synergistically enhanced the catalytic activity and recyclability in organocatalysis. As the aminoclay displayed good water dispersibility, the nanocatalyst indicated satisfactory catalytic performance in the reaction of reducing nitrophenol and nitroanilines to the corresponding aminobenzene derivatives. Meanwhile, the AC@Fe₃O₄@Pd nanocatalyst exhibited excellent reusability, while still maintaining good activity after several catalytic cycles.

Pt incorporated mesoporous carbon spheres: controllable structure with enhanced catalytic activity and stability

We report a simple synthesis process to prepare well-dispersed Pt nanoparticles incorporated in mesoporous carbon spheres. By manipulating the relative ratio of Pt precursor and resorcinol-formaldehyde resin (RF), Pt/carbon composites with different morphologies and Pt content were achieved. The as-prepared Pt/C composite materials show higher catalytic activity and reusability for the reduction of 4-nitrophenol (4-NP) than the Pt deposited commercial activated carbon (Pt/AC), which can be ascribed to the high dispersion of Pt nanoparticles in the carbon spheres.

We report a simple synthesis process to prepare well-dispersed Pt nanoparticles incorporated in mesoporous carbon spheres.

Modification of heterogeneous photocatalysts for selective organic synthesis

This review elaborates on recent strategies of modifying heterogeneous photocatalysts for high-efficiency selective organic synthesis.

Magnetic Co-Doped MoS2 Nanosheets for Efficient Catalysis of Nitroarene Reduction

Co-doped MoS₂ nanosheets have been synthesized through the hydrothermal reaction of ammonium tetrathiomolybdate and hydrazine in the presence of cobalt acetate. These nanosheets exhibit a dominant metallic 1T phase with cobalt ion-activated defective basal planes and S-edges. In addition, the nanosheets are dispersible in polar solvents like water and methanol. With increased active sites, Co-doped MoS₂ nanosheets exhibit exceptional catalytic activity in the reduction of nitroarenes by NaBH₄ with impressive turnover frequencies of 8.4, 3.2, and 20.2 min^-1 for 4-nitrophenol, 4-nitroaniline, and nitrobenzene, respectively. The catalyst is magnetic, enabling its easy separation from the reaction mixture, thus making its recycling and reusability simple and efficient. The enhanced catalytic activity of the Co-doped 1T MoS₂ nanosheets in comparison to that of undoped 1T MoS₂ nanosheets suggests that incorporation of cobalt ions in the MoS₂ lattice is the major reason for the efficiency of the catalyst. The dopant, Co, plays a dual role. In addition to providing active sites where electron transfer is assisted through redox cycling, it renders the nanosheets magnetic, enabling their easy removal from the reaction mixture.