Highly Efficient Silver Catalyst Supported by a Spherical Covalent Organic Framework for the Continuous Reduction of 4-Nitrophenol

Solid Handmade Ternary Coinage Metal Mentors for Organic Bond-Making and Bond-Breaking Applications

A comparative approach is employed for the novel synthesis of a magnetically recoverable ternary nanocomposite consisting of g-C3N4-supported Fe3O4 decorated with coinage metals (Au, Ag, and Cu). This synthesis is achieved through a straightforward and convenient one-step grinding protocol. In situ, the nanoparticles were grown on the g-C3N4-assist Fe3O4 matrix (GCFM), and the agglomeration of these nanoparticles on the matrix creates a pathway for the formation of the nanocomposite (NC). The as-formed CNC was confirmed with the help of characterization analyses, namely XRD, FT-IR, HR-TEM, FE-SEM, XPS, VSM, UV-vis, and NMR studies. Together with NPs and GCFM, with the quantum consequence, the activity of the NC shows better electron transfer via transfer of electrons, which grabs tremendous attention toward it, resulting in enhanced plausible photocatalytic degradation toward pharmaceutical compounds, dyes, and anthropogenic pollutants. The activity of the C-NC hikes at 88% for ciprofloxacin (CX) and 90% for paracetamol (PM); furthermore, the activity of the C-NC hikes at 88% and 87% for xylene Cyanol FF (XCF) and malachite green (MLG), respectively. Interestingly, an added advantage is the formation of a C-C bond (homocoupling reaction) in phenylboronic acid (PA) via a greener solvent under ambient conditions. The yield percentage of the conversion product shows satisfactory results, and its reproducibility was good for the prepared ternary NC. The conversion treatment of anthropogenic pollutants, namely 4-nitrophenol, grasps a high percentage (98%). In addition, the NC shows good activity toward both types of bacteria. The reproducibility of the composite also shows virtuous activity against pharmaceutical as well as toxic contaminants. The as-prepared CNC was specifically engineered to perform both bond formation and bond cleavage of organic molecules under ambient conditions for multiple cycles.

Covalent Organic Framework Nanoarchitectonics: Recent Advances for Precious Metal Recovery

The recovery of precious metals (PMs) from secondary resources has garnered significant attention due to environmental and economic considerations. Covalent organic frameworks (COFs) have emerged as promising adsorbents for this purpose, owing to their tunable pore size, facile functionalization, exceptional chemical stability, and large specific surface area. This review provides an overview of the latest research progress in utilizing COFs to recover PMs. Firstly, the design and synthesis strategies of chemically stable COF-based materials, including pristine COFs, functionalized COFs, and COF-based composites, are delineated. Furthermore, the application of COFs in the recovery of gold, silver, and platinum group elements is delved into, emphasizing their high adsorption capacity and selectivity as well as recycling ability. Additionally, various interaction mechanisms between COFs and PM ions are analyzed. Finally, the current challenges faced by COFs in the field of PM recovery are discussed, and potential directions for future development are proposed, including enhancing the recyclability and reusability of COF materials and realizing the high recovery of PMs from actual acidic wastewater. With the targeted development of COF-based materials, the recovery of PMs can be realized more economically and efficiently in the future.

Catalyst-On-Hotspot Nanoarchitecture: Plasmonic Focusing of Light onto Co-Photocatalyst for Efficient Light-To-Chemical Transformation

Plasmon-mediated catalysis utilizing hybrid photocatalytic ensembles promises effective light-to-chemical transformation, but current approaches suffer from weak electromagnetic field enhancements from polycrystalline and isotropic plasmonic nanoparticles as well as poor utilization of precious co-catalyst. Here, efficient plasmon-mediated catalysis is achieved by introducing a unique catalyst-on-hotspot nanoarchitecture obtained through the strategic positioning of co-photocatalyst onto plasmonic hotspots to concentrate light energy directly at the point-of-reaction. Using environmental remediation as a proof-of-concept application, the catalyst-on-hotspot design (edge-AgOcta@Cu2O) enhances photocatalytic advanced oxidation processes to achieve superior organic-pollutant degradation at ≈81% albeit having lesser Cu2O co-photocatalyst than the fully deposited design (full-AgOcta@Cu2O). Mass-normalized rate constants of edge-AgOcta@Cu2O reveal up to 20-fold and 3-fold more efficient utilization of Cu2O and Ag nanoparticles, respectively, compared to full-AgOcta@Cu2O and standalone catalysts. Moreover, this design also exhibits catalytic performance >4-fold better than emerging hybrid photocatalytic platforms. Mechanistic studies unveil that the light-concentrating effect facilitated by the dense electromagnetic hotspots is crucial to promote the generation and utilization of energetic photocarriers for enhanced catalysis. By enabling the plasmonic focusing of light onto co-photocatalyst at the single-particle level, the unprecedented design offers valuable insights in enhancing light-driven chemical reactions and realizing efficient energy/catalyst utilizations for diverse chemical, environmental, and energy applications.

Fast synthesis of nanoporous Cu/Ag bimetallic triangular nanoprisms via galvanic replacement for efficient 4-nitrophenol reduction

We report the synthesis of nanoporous Cu/Ag bimetallic triangular nanoprisms (BTNPs) using a galvanic replacement method. Based on ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS) analyses, the structure of Cu/Ag BTNPs was characterized. The prepared Cu/Ag BTNPs exhibited excellent catalytic activity and good cycling stability for the reduction of 4-nitrophenol (4-NP) due to the synergistic effect between Cu and Ag elements. The kinetic rate constant (k) and turnover frequency (TOF) values reached 331 × 10-3 s-1 and 500 × 10-3 s-1, respectively, which were higher than those of previously reported Cu, Ag, Au, Cu/Ag or Cu/Au-based catalysts. We hope that the development of promising routes for high-quality BTNPs can broaden their applications in catalysis and environmental sustainability.

Covalent Organic Framework Impregnated with Silver and Copper Nanoparticles: An Advanced Approach for Catalytic Degradation of Organic Pollutants in Wastewater

In this study, we introduce an economically viable and scalable process for developing a novel covalent organic framework (COF), which is a cross-linked polymer. The resulting material, TzTFB-COF, is successfully functionalized with silver and copper nanoparticles, which show high adequacy in the degradation of nitroaromatic compounds (NACs). For the synthesis of TzTFB-COF, s-tetrazine diamine (Tz) and 1,3,5-triformylbenzene (TFB) are chosen as building blocks, which exhibit a high density of nitrogen-containing sites. TzTFB-COF shows good chemical and thermal stability (>300 °C). For functionalization of TzTFB-COF with silver and copper nanoparticles, a solution infiltration technique is used. The composite materials, i.e., Ag@TzTFB-COF and Cu@TzTFB-COF, have been characterized using various spectroscopic and analytical techniques, which show high activity, high selectivity, and excellent chemical and thermal stability up to 350 °C. The silver and copper contents of Ag@TzTFB-COF and Cu@TzTFB-COF are determined to be 9.6 and 12.4 wt % by inductively coupled plasma optical emission spectrometer (ICP-OES). The catalytic efficiency of the synthesized Ag@TzTFB-COF and Cu@TzTFB-COF materials is assessed in the context of catalyzing the hydrogenation of NACs. Experimental results reveal a remarkable catalytic performance when conducted in an aqueous medium, and notably, the materials demonstrate substantial potential for reusability across multiple catalytic cycles. The determined parameters for the catalytic hydrogenation reaction, i.e., the rate constants and Gibbs free energies, are found to be 0.0185 s-1 and 9.878 kJ/mol for Ag@TzTFB-COF and 0.0219 s-1 and 9.615 kJ/mol for Cu@TzTFB-COF. Thus, the catalytic reaction exhibits characteristics of endothermic, endergonic, and nonspontaneous nature.

An interfacial synergism effect of Pd-g-C3N4 in Pd/g-C3N4 for highly active and selective hydrogenation of 4-nitrophenol

Herein, we report that Pd nanoparticles (NPs) anchored on graphitic nitride carbon (Pd/g-C3N4) catalysts with various Pd contents (1.55 wt%, 0.14 wt%, 0.04 wt%) are successfully prepared via a simple NaBH4 reduction method, exhibiting excellent catalytic activity and selectivity toward 4-aminophenol (4-AP) in 4-nitrophenol (4-NP) selective hydrogenation. 4-NP is completely converted to 4-AP (yield ∼ 100%) under quite moderate reaction conditions (40 °C, 2.0 MPa H2 and 5 min) over the 1.55 wt% Pd/g-C3N4 catalyst, with a high reaction rate r = 134.4 mol4-NP molPd-1 min-1. The excellent catalytic performance can be attributed to the following reasons: (1) a higher ratio of Pd(0)/Pdn+ provides much more exposed active sites for the potential adsorption and activation of the reactants, which is beneficial for increasing the reaction rate and catalytic activity; (2) Pd NPs are highly dispersed on g-C3N4 due to the strong interaction of Pd-N or Pd-C; (3) the interfacial synergism effect between Pd NPs and g-C3N4 enables the effective adsorption and activation of H2 (4-NP) at Pd (g-C3N4), promoting the catalytic hydrogenation of 4-NP and improving their catalytic properties. In addition, this catalyst has superior reusability.

Synthesis and characterization of Pd0 nanoparticles supported over hydroxyapatite nanospheres for potential application as a promising catalyst for nitrophenol reduction

Nitrophenols, which are defined as an important toxic and carcinogenic pollutant in agricultural and industrial wastewater due to their solubility in water, form of resistance against all organisms in water resources. It is vital that these compounds, which are highly toxic as well as highly explosive, are removed from the aquatic ecosystem. In this paper, we reported the preparation and advanced characterization of Pd0 nanoparticles supported over hydroxyapatite nanospheres (Pd0@nano-HAp). The catalytic efficiency of the Pd0@nano-HAp catalyst was examined in the reduction of nitrophenols in water in the presence of NaBH4 as reducing agent and the great activity of catalyst have been specified against 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol and 2,4,6-trinitrophenol compounds with 70.6, 82.4, 27.6 and 41.4 min-1 TOFinitial values, respectively. Another important point is that the Pd0@nano-HAp catalyst has perfect reusability performance (at 5th reuse between 68.5 and 92.8 %) for the reduction of nitrophenols. In addition, catalytic studies were carried out at different temperatures in order to determine thermodynamic parameters such as Ea, ΔH≠ and ΔS≠.

Covalent organic framework-supported ultrasmall Rh nanoparticles as peroxidase mimics for colorimetric sensing of cysteine

Covalent organic frameworks (COFs), as a novel porous organic polymer with periodic and highly ordered structure, are ideal carrier matrix for metal nanoparticles due to high specific surface area, good stability, controllable pore size, and structural tunability. In this work, COFs are used as a carrier to in-situ grow ultrasmall rhodium nanoparticles (Rh NPs, ∼2.4 nm), which are uniformly distributed in the pores and on the surfaces of the COFs. The formed composite (COF-Rh) shows excellent peroxidase-mimetic activity benefiting from the good catalytic activity of ultrafine and highly dispersed Rh NPs as well as the high affinity of COFs to organic molecules (i.e., catalytic substrates). Cysteine (Cys) can inhibit the peroxidase-like activity of COF-Rh due to the interaction of -SH in Cys with Rh and the reduction of oxidized peroxidase substrate by Cys. By regulating the peroxidase-like activity of the system, a colorimetric method is successfully developed for Cys detection. Using smartphone as a readout, a portable strategy is further proposed for rapid and visual sensing of Cys.

Green preparation of silver nanocluster composite AgNCs@CF-g-PAA and its application: 4-NP catalytic reduction and hydrogen production

4-Nitrophenol (4-NP) is a serious organic environmental pollutant. Conversion of 4-nitrophenol to 4-aminophenol (4-AP) by catalytic hydrogenation is an effective solution. In this work, a catalyst (AgNCs@CF-g-PAA) loaded with silver nanoclusters (AgNCs) was prepared by radiation technique. Firstly, the template polyacrylic acid (PAA) was grafted onto the cotton fiber (CF) by radiation grafting technique to obtain a solid template (CF-g-PAA). After that, AgNCs were synthesized in situ on CF-g-PAA by radiation reduction, and the composite material AgNCs@CF-g-PAA was obtained directly. AgNCs@CF-g-PAA has an obvious photoluminescence phenomenon, which is attributed to the stable AgNCs binding to the carboxyl on the PAA molecular chain. Due to the extremely small size of AgNCs, AgNCs@CF-g-PAA has good catalytic characteristics. The prepared AgNCs@CF-g-PAA catalyst has a very high catalytic rate for the hydrogenation of 4-NP. Even at high concentrations of 4-NP, AgNCs@CF-g-PAA can still maintain a high catalytic rate. At the same time, the AgNCs@CF-g-PAA catalyst can also be used to catalyze the rapid hydrolysis of sodium borohydride, which is conducive to hydrogen production. In summary, we have prepared a practical catalyst AgNCs@CF-g-PAA with high catalytic performance based on cheap raw materials and a simple synthesis route, which provides a catalyst candidate for the treatment of water contaminant 4-NP and the production of hydrogen from sodium borohydride.

Rapid biosynthesis and characterization of metallic gold nanoparticles by olea europea and their potential application in photoelectrocatalytic reduction of 4-nitrophenol

In recent years, photoelectrocatalysis of gold nanoparticles (Au NPs) has received considerable attention due to their potential to improve catalytic efficiency. Herein, ultra-small Au NPs were successfully synthesized in a single pot using olea europea leaf extract as a green reducing agent for the degradation of 4-nitrophenol. The TEM images showed uniform distribution and spherical shape of Au NPs with an average diameter of 5 nm. Taking advantage of the ability of Au nanoparticles to absorb visible and near-infrared light, 4-nitrophenol can be successfully reduced in the presence of NaBH₄. Additionally, the electrochemical activity of the fabricated Au photocathode was investigated by linear sweep voltammetry in the dark and at VIS-NIR light irradiation. This showed an increased photocurrent density of 27 mA cm^-2 with an onset potential of -0.71 V. This indicates that the Au photocathode is highly active at VIS-NIR light. Interestingly, the Au photocathode showed a higher current density of 37 mA cm^-2 with an onset potential of -0.6 V in the presence of 4-nitrophenol during VIS-NIR irradiation, indicating that 4-nitrophenol was efficiently reduced by the photocathode. The Au photocathode completely reduced 4-nitrophenol in the wastewater within 35 min. Recyclability studies showed that the Au NPs photocathode exhibited higher stability over multiple cycles, confirming the ability of the electrode to treat wastewater over a longer period of time. This study demonstrates the effectiveness of the photoelectrochemical (PEC) process in reducing organic compounds in wastewater.

Space-confined growth of nanoscale metal-organic frameworks/Pd in hollow mesoporous silica for highly efficient catalytic reduction of 4-nitrophenol

The development of confined growth of metal-organic frameworks (MOFs) in a nano-space remains a challenge mainly due to the spatial size randomness and inhomogeneity of host materials and the limitation of MOF species. In this study, we developed a general "stepwise vacuum evaporation" strategy, which allows the nano-confined growth of MOFs in hollow mesoporous silica nanospheres (HMSN) by the vacuum forces and the capillary effect. A series of nanoscale MOFs including ZIF-8, ZIF-90, HKUST-1, MIL-53(Cr) and UiO-66-NH2 were confinely synthesized inside the cavities of HMSN, resulting in hierarchically porous composites with core-shell structures. Further functionalization was studied by anchoring Pd to obtain UiO-66-NH2/Pd@HMSN catalyst, which exhibited excellent activity in the catalytic reduction of 4-nitrophenol to 4-aminophenol under ambient condition.

Recyclable Mussel-Inspired Magnetic Nanocellulose@Polydopamine-Ag Nanocatalyst for Efficient Degradation of Refractory Organic Pollutants and Bacterial Disinfection

Development of a novel strategy to tackle bacterial-contaminated complex industrial wastewaters containing refractory organic pollutants is of great demand. In this study, polydopamine (PDA)-coated magnetic cellulose nanofiber (MCNF)-loaded silver nanoparticle (AgNP) (MCNF/PDA-Ag) nanocomposites were designed and applied for efficient degradation of organic dye pollutants and inactivation of Escherichia coli (E. coli) in wastewater. In the presence of NaBH₄, MCNF/PDA-Ag could achieve a high catalytic reduction rate of 6.54 min^-1 for the removal of methylene blue. Similarly, it showed good catalytic reduction performance for methyl orange (0.63 min^-1) and 4-nitrophenol (2.94 min^-1). The MCNF/PDA-Ag nanocomposites can be easily magnetically recycled and reused with negligible loss of catalytic performance. Moreover, this nanocatalyst also exhibited excellent disinfection performance against E. coli, with more than 99% disinfection ratio at very low doses (50 μg/mL). Overall, this work provides new insights into a delicate design of advanced magnetically recyclable silver nanocomposites with ultrahigh catalytic rates and excellent antibacterial properties from sustainable nature biomass.

Metalated covalent organic frameworks: from synthetic strategies to diverse applications

Covalent organic frameworks (COFs) are a class of organic crystalline porous materials discovered in the early 21st century that have become an attractive class of emerging materials due to their high crystallinity, intrinsic porosity, structural regularity, diverse functionality, design flexibility, and outstanding stability. However, many chemical and physical properties strongly depend on the presence of metal ions in materials for advanced applications, but metal-free COFs do not have these properties and are therefore excluded from such applications. Metalated COFs formed by combining COFs with metal ions, while retaining the advantages of COFs, have additional intriguing properties and applications, and have attracted considerable attention over the past decade. This review presents all aspects of metalated COFs, from synthetic strategies to various applications, in the hope of promoting the continued development of this young field.

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).

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.

Synthesis of Biogenic Silver Nanocatalyst and their Antibacterial and Organic Pollutants Reduction Ability

Plant-mediated nanoparticles are gaining popularity due to biologically active secondary metabolites that aid in green synthesis. This study describes a simple, environmentally friendly, dependable, and cost-effective production of silver nanoparticles utilizing Cucumis sativus and Aloe vera aqueous leaf extracts. The aqueous leaf extracts of Cucumis sativus and Aloe vera, which worked as a reducing and capping agent, were used to biosynthesize silver nanoparticles (AgNPs). The formation of surface plasmon resonance peaks at 403 and 405 nm corresponds to the formation of colloidal Ag nanoparticles. Similarly, the Bragg reflection peaks in X-ray diffraction patterns observed at 2θ values of 38.01°, 43.98°, 64.24°, and 77.12° representing the planes of [111], [200], [220], and [311] correspond to the face-centered cubic crystal structure of silver nanoparticles. Fourier transform infrared spectroscopy confirms that bioactive chemicals are responsible for the capping of biogenic silver nanoparticles. The size, structure, and morphology of AgNPs with diameters ranging from 8 to 15 nm were examined using transmission electron microscopy. Water contamination by azo dyes and nitrophenols is becoming a more significant threat every day. The catalytic breakdown of organic azo dye methyl orange (MO) and the conversion of para-nitrophenol (PNP) into para-aminophenol using sodium borohydride was evaluated using the prepared biogenic nanoparticles. Our nanoparticles showed excellent reduction ability against PNP and MO with rate constants of 1.51 × 10^-3 and 6.03 × 10^-4s^-1, respectively. The antibacterial activity of the nanomaterials was also tested against four bacteria: Staphylococcus aureus, Klebsiella pneumoniae, Enterobacter, and Streptococcus pneumoniae. These biogenic AgNPs displayed effective catalytic and antibacterial characteristics by reducing MO and PNP and decreasing bacterial growth.

A hydroxy-containing three dimensional covalent organic framework bearing silver nanoparticles for reduction of 4-nitrophenol and degradation of organic dyes

A hydroxy-containing three dimensional covalent organic framework bearing Ag nanoparticles for catalytic reduction of 4-nitrophenol and degradation of methylene blue and Congo red.

Magnetic covalent organic framework immobilized gold nanoparticles with high-efficiency catalytic performance for chemiluminescent detection of pesticide triazophos

Covalent organic frameworks (COFs) are considered to be a promising support material for catalyst due to their highly ordered porous structure. Here, a core-shell structured Fe₃O₄ magnetic covalent organic framework (Fe₃O₄@COF) was synthesized and employed to provide basic sites for immobilization of gold nanoparticles (AuNPs). The AuNPs was in-situ immobilized on the shell of Fe₃O₄@COF via a citrate reducing method. The Fe₃O₄@COF-AuNP had convenient magnetic separability and exhibited excellent mimicking peroxidase-like activity in catalyzing chemiluminescence (CL) reaction of luminol with hydrogen peroxide (H₂O₂). With acetylcholine chloride (ACh) as substrate of acetylcholinesterase (AChE), a CL method was exploited for sensitive detection of organophosphorus pesticide triazophos due to its irreversible inhibiting effect on the AChE activity and subsequently influences the production of H₂O₂ under the condition of choline oxidase (ChOx). This method gave a good linearity for triazophos in the range of 5.0-300.0 nmol L^-1, and a limit of detection (LOD) of 1 nmol L^-1 was acquired. The applicability of this method was verified by the determination of triazophos in different spiked vegetable samples.

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.

Smart hydrogel-microsphere embedded silver nanoparticle catalyst with high activity and selectivity for the reduction of 4-nitrophenol and azo dyes

A simple method is reported for the preparation of silver nanoparticle (AgNP) embedded pH-responsive hydrogel microparticle catalyst via Michael addition gelation and in-situ silver nitrate (AgNO₃) reduction. The AgNP-hydrogel microsphere exhibited an efficient reduction of pollutants like 4-Nitrophenol (4-NP) and Congo red (CR) under acidic medium with turn over frequency (TOF) of ~170 h^-1 and ~124 h^-1 respectively. Interestingly, the activity of the catalysts was turned-OFF under a basic medium (≥ pH 12) due to the deswelling pH-responsive matrix surrounding the AgNPs. On the contrary, turning-OFF the hydrogenation of a cationic pollutant like methylene blue (MB) using high pH (≥ 12) was not possible, due to ionic interaction of MB molecules with the negatively charged catalyst at this pH. This feature was used to demonstrate selective hydrogenation of only MB from a mixture of 4-NP and MB. Finally, five recycling steps confirmed the reusability and practical application potential of the catalyst.