Sustainable Catalytic Activity of Ag-Coated Chitosan-Capped γ-Fe2O3 Superparamagnetic Binary Nanohybrids (Ag-γ-Fe2O3@CS) for the Reduction of Environmentally Hazardous Dyes-A Kinetic Study of the Operating Mechanism Analyzing Methyl Orange Reduction

Green synthesis of silver nanoparticles-capped aminated lignin as a robust active catalyst for dye discoloration

Considering the severity of global environmental issues, biomass-derived products have received significant attention as alternatives to foster sustainability and eco-friendliness. The use of metal nanoparticle catalysts for dye decomposition is emerging as a promising approach for environmentally friendly dye removal. In this study, an aminosilane-modified lignin (AML)/silver nanoparticle (AgNP) composite was fabricated and used as a hydrogenation catalyst. The AgNPs were well dispersed on the AML surface and formed strong bonds within the AML/AgNP complex. AML also served as an effective reducing and capping agent for Ag(I) ions. The AML/AgNPs were found to be an efficient catalyst with excellent dye degradation ability and easy reusability. Biomass-derived lignin can be used as a reducing and capping agent for metals and this complex can be used as a high-value bio-catalyst for wastewater remediation.

Lignin-functionalized cobalt for catalytic reductive degradation of organic dyes in simple and hybrid binary systems

To fulfill the unprecedented valorization approaches for lignocellulose, this work focuses on the potential of lignin-derived catalytic systems for bio-remediation, which are natural materials perceived to address the increased demand for eco-conscious catalyzed processes. A useful lignin-functionalized cobalt (Lig-Co) catalyst has been prepared, well-characterized and deployed for the catalyzed reducing decomposition of stable harmful organic pollutants such as methylene blue (MB) and methyl orange (MO), in simple and binary systems. The multifunctional character of lignin and the presence of various active sites can promote effectively loaded metal nanoparticles (NPs). Considerably, optimizing detoxification tests showed that the uncatalyzed use of NaBH4 as a reductive agent led to an incomplete reduction of organic contaminants over a long period of up to 65 min. Interestingly, Lig-Co catalyst exhibited a high reduction rate and turnover frequency of up to 99.23% and 24.12 min-1 for MB, respectively, while they reached 99.25% and 26.21 min-1 for MO at normal temperature. Kinetically quick catalytic reaction was also demonstrated for the hybrid system, in which the rate constant k was 0.175 s-1 and 0.165 s-1 for MB and MO, respectively, within a distinctly low reaction time of around 120 s. The reproducibility of the Lig-Co catalyst induces a desirable capacity to reduce stable dyes present simultaneously in the binary system, with 6 successive catalytic runs and over 80% of activity retained. Such robust findings underline the considerable interest in developing future lignin-mediated catalytic transformations and upscaling biomass-derived products, to meet the growing demand for sustainable and eco-friendly alternatives in various industries.

Burdock-Derived Composites Based on Biogenic Gold, Silver Chloride and Zinc Oxide Particles as Green Multifunctional Platforms for Biomedical Applications and Environmental Protection

Green nanotechnology is a rapidly growing field linked to using the principles of green chemistry to design novel nanomaterials with great potential in environmental and health protection. In this work, metal and semiconducting particles (AuNPs, AgClNPs, ZnO, AuZnO, AgClZnO, and AuAgClZnO) were phytosynthesized through a "green" bottom-up approach, using burdock (Arctium lappa L.) aqueous extract. The morphological (SEM/TEM), structural (XRD, SAED), compositional (EDS), optical (UV-Vis absorption and FTIR spectroscopy), photocatalytic, and bio-properties of the prepared composites were analyzed. The particle size was determined by SEM/TEM and by DLS measurements. The phytoparticles presented high and moderate physical stability, evaluated by zeta potential measurements. The investigation of photocatalytic activity of these composites, using Rhodamine B solutions' degradation under solar light irradiation in the presence of prepared powders, showed different degradation efficiencies. Bioevaluation of the obtained composites revealed the antioxidant and antibacterial properties. The tricomponent system AuAgClZnO showed the best antioxidant activity for capturing ROS and ABTS•⁺ radicals, and the best biocidal action against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The "green" developed composites can be considered potential adjuvants in biomedical (antioxidant or biocidal agents) or environmental (as antimicrobial agents and catalysts for degradation of water pollutants) applications.

Green Synthesis and Antibacterial Activity of Ag/Fe2O3 Nanocomposite Using Buddleja lindleyana Extract

In the study reported in this manuscript, silver/iron oxide nanocomposites (Ag/Fe₂O₃) were phytosynthesized using the extract of Buddleja lindleyana via a green, economical and eco-friendly strategy. The biosynthesized Ag/Fe₂O₃ nanocomposites were characterized using UV-Vis spectrophotometry, FTIR, XRD, TEM, DLS and SEM-EDX analyses. The particulates showed a triangular and spherical morphology having sizes between 25 and 174 nm. FTIR studies on the nanoparticles showed functional groups corresponding to organic metabolites, which reduce and stabilize the Ag/Fe₂O₃ nanocomposite. The antimicrobial efficacy of the phytosynthesized Ag/Fe₂O₃ against bacterial pathogens was assessed. In addition, Ag/Fe₂O₃ exhibited broad spectrum activities against B. subtilis, S. aureus, E. coli, and P. aeruginosa with inhibition zones of 23.4 ± 0.75, 22.3 ± 0.57, 20.8 ± 1.6, and 19.5 ± 0.5 mm, respectively. The Ag/Fe₂O₃ composites obtained showed promising antibacterial action against human bacterial pathogens (S. aureus, E. coli, B. subtilis and P. aeruginosa), making them candidates for medical applications.

Nickel foam supported porous copper oxide catalysts with noble metal-like activity for aqueous phase reactions

Contiguous metal foams offer a multitude of advantages over conventional powders as supports for nanostructured heterogeneous catalysts; most critically a preformed 3-D porous framework ensuring full directional coverage of supported catalyst, and intrinsic ease of handling and recyclability. Nonetheless, metal foams remain comparatively underused in thermal catalysis compared to more conventional supports such as amorphous carbon, metal oxides, zeolites and more recently MOFs. Herein, we demonstrate a facile preparation of highly-reactive, robust, and easy to handle Ni foam-supported Cu-based metal catalysts. The highly sustainable synthesis requires no specialized equipment, no surfactants or additive redox reagents, uses water as solvent, and CuCl2(H2O)2 as precursor. The resulting material seeds as well-separated micro-crystalline Cu2(OH)3Cl evenly covering the Ni foam. Calcination above 400 °C transforms the Cu2(OH)3Cl to highly porous CuO. All materials display promising activity towards the reduction of 4-nitrophenol and methyl orange. Notably, our leading CuO-based material displays 4-nitrophenol reduction activity comparable with very reactive precious-metal based systems. Recyclability studies highlight the intrinsic ease of handling for the Ni foam support, and our results point to a very robust, highly recyclable catalyst system.

Ag nanoparticles anchored on NiO octahedrons (Ag/NiO composite): An efficient catalyst for reduction of nitro substituted phenols and colouring dyes

The development of an efficient sustainable catalyst for effective removal of hazardous chemicals, viz. nitrophenols and organic dyes, from wastewater is a challenging task. Herein, facile synthesis of Ag/NiO composites by anchoring Ag nanoparticles (NPs) on NiO octahedrons with different amounts of Ag NPs (AN-5% (5% Ag), AN-10% (10% Ag) and AN-15% (15% Ag)) has been demonstrated. SEM (scanning electron microscopic) and TEM (transmission electron spectroscopic) images ensured the proper anchoring of spherical Ag NPs (particle size = 16.54 ± 1.88 nm) on octahedron particles of NiO, which was also ensured by XPS (X-ray photoelectron spectroscopy) analysis. Moreover, the resulting composites have an average surface area (49-52 m²g^‒1) and pore size (2.39-2.26 nm). All three synthesized Ag/NiO composites (100 μL) catalyzed the complete reduction of para-np (4-nitrophenol: 0.1587 mM) within 2-3 min in the presence of 0.04 M NaBH₄. Among them, AN-5% has been chosen because of the lowest anchored Ag (5%) to obtain the optimized catalyst's amount (50 μL) and concentration of para-np (0.1587 mM). AN-5% also exhibited excellent catalytic activity towards different nitro substituted phenols, viz. ortho-np (2-nitrophenol), meta-np (3-nitrophenol), para-np (4-nitrophenol) and tri-np (2,4,6-trinitrophenol). AN-5% displayed ∼100% catalytic efficiency for reducing meta-np in 2 min with the apparent first order rate constant (k_app) and normalized rate constant (K_nor) as 1.99 s^-1 and 398.14 s^-1 g^-1, respectively. Additionally, AN-5% (29.41 μg mL^-1) reduced >95% of the colouring dyes (10 ppm) such as CONG-R (congo red: 95% in 6 min), METH-O (methyl orange: 97.5% in 7 min), METH-B (methylene blue: 98.3% in 10 min) and RHOD-B (rhodamine B: 99.2% in 5 min). AN-5% not only demonstrated catalytic reduction towards individual pollutants, but also showed excellent activity for reduction of the mixtures of nitrophenols/dyes and for treatment of simulated industrial effluent samples (EFF1, EFF2) and a real industrial sample (textile dye-bath effluent). AN-5% can also be reused up to several cycles with almost same efficiency and followed the Langmuir-Hinshelwood apparent first order kinetics model.

Electrostatic Interaction-Controlled Formation of Pickering Emulsion for Continuous Flow Catalysis

Although noble metal or non-noble metal-catalyzed reactions are widely used, it is still difficult to apply these reactions in the large-scale synthesis of chemicals because most of the reactions are carried out by the inefficient batch reaction strategy. Herein, Pickering emulsion-based continuous flow catalysis was utilized to address this problem. Cellulose nanofibers with aldehyde groups (ACNF) were generated through oxidizing C2 and C3 hydroxyl groups of cellulose nanofibers into aldehyde groups by NaIO₄, followed by in situ depositing Ag nanoparticles on ACNF to produce Ag-decorated ACNF (ACNF@Ag) via a facile aldehyde-induced reduction method. ACNF@Ag with ∼2 wt % Ag (ACNF@Ag2) has been used to prepare the Pickering emulsion by controlling the electrostatic interaction between ACNF@Ag2 and the oil-water interface via adjusting the pH. It was found that the Pickering emulsion could be generated at a pH around 3.29 and was determined to be the oil-in-water emulsion. The reduction of organic molecules (4-nitrophenol (4-NP), methylene blue (MB), and methyl orange (MO)) was selected as a model reaction to test the reliability of the Pickering emulsion in continuous flow catalysis, which demonstrated very high conversion rates for 4-NP (>98%, 50 h), MB (>99%, 30 h), and MO (>96%, 40 h).

Decorated Au NPs on agar modified Fe3O4 NPs: Investigation of its catalytic performance in the degradation of methylene orange, and anti-human breast carcinoma properties

This work describes an eco-friendly approach for in situ immobilization of Au nanoparticles on the surface of Fe₃O₄ nanoparticles, with help of Agar and ultrasound irradiations, without using any toxic reducing and capping agents. The structure, morphology, and physicochemical properties were characterized by various analytical techniques such as Fourier transformed infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), inductively coupled plasma (ICP) and vibrating sample magnetometer (VSM). The desired catalyst showed great efficiency in the reductive degradation of methylene orange (MO) dye over NaBH₄ at room temperature. The MO was fully reduced in only 70 s and achieved rate constant of 9.6 × 10^-2 s^-1. The catalyst was reused for 10 runs without significant loss in catalytic activity. Cell viability of Fe₃O₄/agar/Au NPs was very low against breast adenocarcinoma (MCF7), breast carcinoma (Hs 578Bst), infiltrating ductal cell carcinoma (Hs 319.T), and metastatic carcinoma (MDA-MB-453) cell lines without any cytotoxicity on the normal cell line. According to the above findings, the Fe₃O₄/agar/Au NPs may be administrated for the treatment of several types of human breast carcinoma in humans.

Bio-assisted synthesized Pd nanoparticles supported on ionic liquid decorated magnetic halloysite: an efficient catalyst for degradation of dyes

Using natural materials, i.e. halloysite nanoclay that is a biocompatible naturally occurring clay and Heracleum persicum extract that can serve as a green reducing agent, a novel magnetic catalyst, Fe₃O₄/Hal-Mel-TEA(IL)-Pd, has been designed and fabricated. To prepare the catalyst, halloysite was first magnetized (magnetic particles with mean diameter of 13.06 ± 3.1 nm) and then surface functionalized with melamine, 1,4 dibromobutane and triethanolamine to provide ionic liquid on the halloysite surface (5 wt%). The latter was then used as a support to immobilize Pd nanoparticles that were reduced by Heracleum persicum extract. The characterization of the catalyst established that the loading of Pd in Fe₃O₄/Hal-Mel-TEA(IL)-Pd was very low (0.93 wt%) and its specific surface area was 63 m²g⁻¹. Moreover, the catalyst showed magnetic property (Ms = 19.75 emu g⁻¹) and could be magnetically separated from the reaction. The catalytic performance of the magnetic catalyst for reductive degradation of methyl orange and rhodamine B in the presence of NaBH₄ in aqueous media was investigated. The activation energy, enthalpy, and entropy for the reduction of methyl orange were estimated as 42.02 kJ mol⁻¹, 39.40 kJ mol⁻¹, and −139.06 J mol⁻¹ K⁻¹, respectively. These values for rhodamine B were calculated as 39.97 kJ mol⁻¹, 34.33 kJ mol⁻¹, and −155.18 Jmol⁻¹K⁻¹, respectively. Notably, Fe₃O₄/Hal-Mel-TEA(IL)-Pd could be reused for eight reaction runs with negligible loss of the catalytic activity (~3%) and Pd leaching (0.01 wt% of the initial loading).

Photocatalytic degradation of malachite green dye using chitosan supported ZnO and Ce-ZnO nano-flowers under visible light

Two types of chitosan-based composites (chitosan/ZnO and chitosan/Ce-ZnO composites) were synthesized under microwave irradiation and characterized as advanced catalysts of enhanced photocatalytic activity under the visible light. The morphological investigation reflected the formation of ZnO and Ce doped ZnO at stunning micro flowers of nano limps. Additionally, the optical studies reflected a reduction in the bandgap of ZnO from 3.3 eV to 2.85 eV and 2.5 eV after supporting it onto chitosan chains and after doping it with cerium, respectively. The synthetic composites were applied in photocatalytic removal of malachite green dye under a visible light source. The synthetic CH/ZnO and CH/Ce-ZnO showed enhancement in the photocatalytic removal of M.G by 54% and 87%, respectively, as compared to the pure ZnO. The synthetic composites are of high stability and can be reused for five photocatalytic degradation cycles at stunning removal percentages. The main oxidizing radicals during the removal of M.G by CH/ZnO are the generated electron-hole pairs as well as the hydroxyl radicals. The effective species in CH/Ce-ZnO photocatalytic system are the photogenerated hydroxyl radicals followed by the electron-hole pairs.