High-efficient catalytic reduction of 4-nitrophenol based on reusable Ag nanoparticles/graphene-loading loofah sponge hybrid

3-D porous cellulose nanofibril aerogels with a controllable copper nanoparticle loading as a highly efficient non-noble-metal catalyst for 4-nitrophenol reduction

Nitrophenols(NPs) are highly toxic compounds that occur in various industrial effluents. Herein, we investigated Cu nanoparticle-loaded cellulose nanofibril (CNF/PEI-Cu) aerogels as a catalyst for degrading 4-nitrophenol (4NP) in the wastewater. Non-noble metal based low-cost catalyst material and easily scalable preparation method make CNF/PEI-Cu aerogel as an appropriate catalyst for practical application in 4NP wastewater treatment. Our strategy to improve the loading amount of homogeneously distributed Cu nanoparticles was to functionalize a CNF aerogel using polyethylene imine (PEI), which can bind Cu²⁺ ions. Porous CNF aerogels with homogenously distributed 20-40 nm Cu nanoparticles were obtained by adsorbing Cu²⁺ ions and chemically reducing them to Cu metal. The FTIR, XRD, SEM, XPS and ICP-OES analysis were used to confirm the in-situ formation of Cu nanoparticles. In the presence of the CNF/PEI-Cu aerogels, 4NP was effectively reduced to 4-aminophenol (4AP) without loss of the Cu nanoparticles. The activation energy (E_a) and reaction rate constant (k_app) of the catalytic 4NP reduction reaction by the CNF/PEI2-Cu aerogels were calculated to be E_a = 39.56 kJ mol^-1 and k_app = 0.770 min^-1, respectively. The E_a is similar or even smaller than the E_a values of the corresponding reactions involving noble-metal catalysts, demonstrating that the CNF/PEI-Cu aerogels developed in the present study have strong potential as practical and economical catalysts.

Role of Lewis Acid Metal Centers in Metal–Organic Frameworks for Ultrafast Reduction of 4-Nitrophenol

Metal–Organic Frameworks (MOFs) can be a good alternative to conventional catalysts because they are non-toxic and can be selective without compromising efficiency. Nano MOFs such as UiO-66 have proven themselves to be competitive in the catalytic family. In this study, we report the excellent catalytic behavior of UiO-66 MOF in the reduction of a model reaction: 4-Nitrophenol (4-NP) to 4-Aminophenol (4-AP) over MOF-5 (Zn-BDC) and MIL-101 (Fe-BDC). Nano UiO-66 crystals were synthesized by a hydrothermal process and characterized by Powder X-ray Diffraction, Diffused Reflectance UV-Vis spectroscopy, Scanning Electron Microscopy, and Transmission Electron Microscopy. The catalysts’ performance during the hydrogenation reduction reaction from 4-NP to 4-AP was investigated in the presence of a reducer, NaBH4. The UiO-66 nano crystals exhibited excellent catalytic behavior owing to its large surface area and Lewis acidic nature at the metal nodes. Furthermore, UiO-66 showed excellent recyclability behavior, verified during repeated consecutive use in a sequence. The catalyst yielded similar catalytic behavior during the reduction of nitrophenols at each cycle, which is a novel finding.

Synthesis and application of CdS nanoparticles-decorated core-shell Ag@Ni nanohybrids for visible-light spectrophotometric assay of sulfide in aqueous sample

Novel Ag@Ni nanosphere decorated with CdS NPs (Ag@Ni-CdS NCs) was synthesized by one step chemical synthesis method. The fabricated NCs were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), fourier transfer infra-red spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), zeta sizer and particle size analyzer. TEM and XRD confirmed the Ag in core and Ni in shell for the effective formation of Ag@Ni core shell nanosphere. EDAX and XPS spectra of NCs confirms the formation of Ag@Ni-CdS NCs. Zeta potential and particle size of the NCs was found to be 29.5 ± 1.5 mV and 24 ± 1 nm respectively. The complete loss in the peak intensity of Ag@Ni-CdS NCs (localized surface plasmon resonance (LSPR)) at ∼410 nm in presence of S^2- ions was observed which indicates its selective detection towards S^2- ions. The sulfide ion sensing by Ag@Ni-CdS NCs was due to the successive oxidation of Ag results in the formulation of Ag²⁺ ions in the system, which causes the diminishing of LSPR band of NCs. The limit of detection (LOD) of S^2- ions by Ag@Ni-CdS NCs was calculated to be of 2.66 nM. The combination of CdS NPs with core-shell Ag@Ni nanosphere guides a promising strategy for S^2- ions detection from environmental polluted samples.

Catalytic reduction of 4-nitrophenol and methylene blue pollutants in water by copper and nickel nanoparticles decorated polymer sponges

In the present study, two catalysts based-on copper and nickel nanoparticles anchored on agarose-coated sponge (Cu-AG-sponge and Ni-AG-sponge) were prepared, respectively. Both catalysts were characterized by analytical techniques of thermogravimetric analysis energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM). Spherical Cu and Ni nanoparticles on struts of AG-coated sponge were observed by FESEM and the samples' elemental composition was confirmed by EDX technique. After characterization, the Cu-AG-sponge and Ni-AG-sponge catalysts were tested in 4-nitrophenol (4-NP) and methylene blue dye (MB) reduction in an aqueous medium. The reduction of the 4-NP to 4-aminophenol (4-AP) was achieved up to 95% using the NaBH₄ reductant and Cu-AG-sponge and Ni-AG-sponge catalysts, respectively. Similarly, the rate of reduction of MB was faster for the Cu-AG-sponge as compared to the Ni-AG-sponge which was discussed based-on the catalyst morphology and other factors. The high rate of reactions for the 4-NP and MB reduction suggests that the Cu-AG-sponge and Ni-AG-sponge catalyst possess high catalytic efficiency, low cost and good reusability having the potential to be used in similar other reactions.

Improving SERS Sensing Efficiency and Catalytic Reduction Activity in Multifunctional Ternary Ag-TiO2-GO Nanostructures: Roles of Electron Transfer Process on Performance Enhancement

Multifunctional nanocomposites have received great attention for years; electron transfer (ET) is considered as an explanatory mechanism for enhancement of performance of these nanostructures. The existence of this ET process has been proved in many studies using either experimental or computational approaches. In this study, a ternary nanocomposite system of Ag/TiO2/GO was prepared to evaluate the performance enhancement in two experimental models: a physical model (i.e., surface-enhanced Raman scattering (SERS) sensor) and a chemical one (i.e., catalytic reduction reaction). The metal/semiconductor heterojunction between Ag and TiO2, as well as Ti-O-C bonds, has allowed plasmonic hot electrons to be transferred in the internal structure of the material. An investigation on the role of Ag content on the SERS sensing and catalytic reduction efficiency of Ag/TiO2/GO was performed in both models. Interestingly, they all resulted in the same optimal Ag content of 50 wt%. It was then further discussed to provide a convincing evidence for the plasmon-induced electron transfer phenomena in the Ag/TiO2/GO nanostructure. These findings also suggest a pathway to design and develop high-performance, cost-effective, facile-preparation, and eco-friendly multifunctional nanostructures for detecting and removing contaminants in environment.

High-efficient reduction of methylene blue and 4-nitrophenol by silver nanoparticles embedded in magnetic graphene oxide

In this study, a ternary magnetically separable nanocomposite of silver nanoparticles (AgNPs) embedded in magnetic graphene oxide (Ag/Fe₃O₄@GO) was designed and synthesized. Beta-cyclodextrin was used as a green reducing and capping agent for decorating of AgNPs on Fe₃O₄@GO. The fabricated material was characterized using X-ray diffractometry, Fourier transform infrared spectroscopy, scanning electron microscopy, vibrating sample magnetometry, and energy-dispersive X-ray spectroscopy. The catalytic properties of the prepared Ag/Fe₃O₄@GO for the reduction of 4-nitrophenol (4-NP) and methylene blue (MB) dye with sodium borohydride were investigated in detail. The morphological and structural studies revealed that Fe₃O₄ and AgNPs with a mean size of 12 nm were uniformly distributed on the GO sheet at high densities. The catalytic tests showed that Ag/Fe₃O₄@GO exhibited an ultrafast catalytic reduction of 4-NP and MB with a reduction rate constant of 0.304 min^-1 and 0.448 min^-1, respectively. Moreover, the catalyst demonstrated excellent stability and reusability, as evidenced by the more than 97% removal efficiency maintained after five reuse cycles. The Ag/Fe₃O₄@GO catalyst could be easily recovered by the magnetic separation due to the superparamagnetic nature of Fe₃O₄ with high saturated magnetization (45.7 emu/g). Besides, the formation of networking between the formed AgNPs and β-CD through hydrogen bonding prevented the agglomeration of AgNPs, ensuring their high catalytic ability. The leaching study showed that the dissolution of Fe and Ag from Ag/Fe₃O₄@GO was negligible, indicating the environmental friendliness of the synthesized catalyst. Finally, the high catalytic performance, excellent stability, and recoverability of Ag/Fe₃O₄@GO make it a potential candidate for the reduction of organic pollutants in wastewater.

Ultrafast conversion of carcinogenic 4-nitrophenol into 4-aminophenol in the dark catalyzed by surface interaction on BiPO4/g-C3N4 nanostructures in the presence of NaBH4

The heterogeneous catalytic conversion of pollutants into useful industrial compounds is a two-goals at once process, which is highly recommended from the environmental, economic, and industrial points of view.

Single source precursor synthesized CuS nanoparticles for NIR phototherapy of cancer and photodegradation of organic carcinogen

Herein, we report cost effective and body compatible CuS nanoparticles (NPs) derived from a single source precursor as photothermal agent for healing deep cancer and photocatalytic remediation of organic carcinogens. These NPs efficiently kill MCF7 cells (both in vivo and in vitro) under NIR irradiation by raising the temperature of tumor cells. Such materials can be used for the treatment of deep cancer as they can produce a heating effect using high wavelength and deeply penetrating NIR radiation. Furthermore, CuS NPs under solar light irradiation efficiently convert p-nitrophenol (PNP), an environmental carcinogen, to p-aminophenol (PAP) of pharmaceutical implication. In a nutshell, CuS can be used for the treatment of deep cancer and for the remediation of carcinogenic pollutants. There seems an intrinsic connection between the two functions of CuS NPs that need to be explored in length.

Ag(I)-Hived Fullerene Microcube as an Enhanced Catalytic Substrate for the Reduction of 4-Nitrophenol and the Photodegradation of Orange G Dye

We report a facile approach to fabricate an Ag-embedded fullerene (C₆₀) catalyst by the chemical reduction of the AgNO₃ complex encapsulated fullerene microcrystal, which showed an enhanced catalytic reduction of 4-nitrophenol because of the strong absorption and propagation of H₂ along the fullerene surface. With the aid of visible-light radiation, photodegradation of orange G dye is achieved through the formation of an electron donor-acceptor dyad between plasmon Ag nanostructures and fullerene molecules, which effectively offsets the "electron-hole" recombination. Neither Ag nanoparticle nor fullerene crystal used in isolation could perform this chemical conversion, implying that the metal-fullerene hybrid structure is imperative for performing the catalytic reaction. The obtained Ag-embedded fullerene crystal is characterized by scanning electron microscopy (SEM), associated energy-dispersive X-ray spectroscopy (EDX) imaging, and X-ray photoelectron spectroscopy (XPS) and demonstrates that the present hybrid materials would add a supplemental member to a family of photocatalysts toward the organic synthesis and wastewater remediation.

Ultrafine bimetallic Ag-doped Ni nanoparticles embedded in cage-type mesoporous silica SBA-16 as superior catalysts for conversion of toxic nitroaromatic compounds

Highly active Ag-doped Ni nanoparticles are successfully fabricated within carboxylic acid (-COOH) functionalized mesoporous silica SBA-16 by a facile wet incipient technique for catalytic conversion of toxic nitroaromatics. The -COOH groups on SBA-16 play a crucial role by enhancing the electrostatic interactions with Ag(I)/Ni(II) cations, that control the crystal growth during the thermal reduction. Systematic characterizations of SBA-16C and Ag_x%Ni@SBA-16C are performed by different techniques including solid state ¹³C and ²⁹Si nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), N₂ sorption, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and superconducting quantum interference device (SQUID). The highly dispersed ultrafine Ag-doped Ni NPs (∼3 nm) are well-confined within SBA-16C and exhibit magnetic properties that are extremely beneficial for recycling. The bimetallic Ag_2.4%Ni@SBA-16C shows exceptionally high catalytic activity during catalytic conversion of toxic nitroaromatics to environmentally friendly amino-aromatics. The enhanced catalytic activity could be ascribed to the combined effects of unique electronic properties, synergistic effects of Ag-doped Ni, ultra-small size, metal loading, and favorable textural properties. These magnetically separable nanocatalysts show excellent durability.

Facile Green Preparation of Rhodium Nanoclusters Supported Nano-Scaled Graphene Platelets for Sonogashira Coupling Reaction and Reduction of p-Nitrophenol

Rhodium nanoclusters were uniformly dispersed on nano-scaled graphene platelets by a simple ‘mix and heat’ method without using any toxic reagents. Distilled water was used to obtain the homogenous dispersion of Rh-nanoclusters on graphene platelets. The morphology of the resultant catalyst (Rh(0)NCs/GNPs) was studied by means of transmission electron microscope (TEM) and atomic force microscope (AFM) analyses. The X-ray photoemission spectroscope (XPS) result confirmed the metallic form of Rh-nanoclusters in Rh(0)NCs/GNPs. The crystalline property and the interaction between Rh-nanoclusters and graphene platelets (GNPs) were studied by means of XRD and Raman analysis. The Rh-loading in Rh(0)NCs/GNPs was confirmed by scanning electron microscope and energy dispersive spectroscope (SEM-EDS) and inductively coupled plasma-mass spectroscope (ICP-MS) analysis. After being optimized, the Rh(0)NCs/GNPs used as catalyst for the reduction of 4-nitrophenol with NaBH4 and the Sonogashira coupling reaction between iodobenzene with phenylacetylene. To our delight, the Rh(0)NCs/GNPs showed excellent catalytic activity towards the reduction of 4-nitrophenol with an excellent turnover frequency (TOF) value of 112.5 min−1. The kapp and k’ values were calculated to be 62.07 × 10−3 min−1(0.002 mg of Rh(0)NCs/GNPs) and 31035 × 10−3 mg−1 min−1,respectively. Alike, under the optimal conditions, the Rh(0)NCs/GNPs gave the desired product, diphenylacetylene, in a good yield of 87% with 91% selectivity. The Rh(0)NCs/GNPs can be reused without significant loss in its catalytic activity.

Green synthesis of Ag@Au bimetallic regenerated cellulose nanofibers for catalytic applications

Highly active and reusable bimetallic Ag@Au/CNC nanocomposite was successfully obtainedviaa simple green synthesis for the reduction of nitrophenol and aza-Michael reaction.