Polydopamine assisted synthesis of ultrafine silver nanoparticles for heterogeneous catalysis and water remediation

Antimicrobial effects of silver nanoparticle-microspots on the mechanical properties of single bacteria

Silver nanoparticles (AgNPs) conjugated with polymers are well-known for their powerful and effective antimicrobial properties. In particular, the incorporation of AgNPs in biocompatible catecholamine-based polymers, such as polydopamine (PDA), has recently shown promising antimicrobial activity, due to the synergistic effects of the AgNPs, silver(I) ions released and PDA. In this study, we generated AgNPs-PDA-patterned surfaces by localised electrochemical depositions, using a double potentiostatic method via scanning electrochemical cell microscopy (SECCM). This technique enabled the assessment of a wide parameter space in a high-throughput manner. The optimised electrodeposition process resulted in stable and homogeneously distributed AgNP-microspots, and their antimicrobial activity against Escherichia coli was assessed using atomic force microscopy (AFM)-based force spectroscopy, in terms of bacterial adhesion and cell elasticity. We observed that the bacterial outer membrane underwent significant structural changes, when in close proximity to the AgNPs, namely increased hydrophilicity and stiffness loss. The spatially varied antimicrobial effect found experimentally was rationalised by numerical simulations of silver(I) concentration profiles.

Silver nanoparticles in plant health: Physiological response to phytotoxicity and oxidative stress

Silver nanoparticles (AgNPs) have gained significant attention in various fields due to their unique properties, but their release into the environment has raised concerns about their environmental and biological impacts. Silver nanoparticles can enter plants following their exposure to roots or via stomata following foliar exposure. Upon penetrating the plant cells, AgNPs interact with cellular components and alter physiological and biochemical processes. One of the key concerns associated with plant exposure to AgNPs is the potential of these materials to induce oxidative stress. Silver nanoparticles can also suppress plant growth and development by disrupting essential plant physiological processes, such as photosynthesis, nutrient uptake, water transport, and hormonal regulation. In crop plants, these disruptions may, in turn, affect the productivity and quality of the harvested components and therefore represent a potential threat to agricultural productivity and ecosystem stability. Understanding the phytotoxic effects of AgNPs is crucial for assessing their environmental implications and guiding the development of safe nanomaterials. By delving into the phytotoxic effects of AgNPs, this review contributes to the existing knowledge regarding their environmental risks and promotes the advancement of sustainable nanotechnological practices.

Bactericidal and biocatalytic temperature responsive microgel based self-cleaning membranes for water purification

The present study focuses on creating an antimicrobial and biocatalytic smart gating membrane by synthesizing unique core-shell microgels. The core-shell microgels are synthesized by grafting short chains of poly(ethylenimine) (PEI) onto a poly((N-isopropyl acrylamide)-co-glycidyl methacrylate)) (P(NIPAm-co-GMA)) core. Subsequently, the produced microgels are utilized as a substrate for synthesizing and stabilizing silver nanoparticles (Ag NPs) through an in-situ approach. These Ag NPs immobilized microgels are then suction filtered over a polyethylene terephthalate (PET) track-etched support to create cross-linked composite microgel membranes (CMMs). After structural and permeation characterization of the prepared CMMs, the laccase enzyme is then covalently grafted to the surface of the membrane and tested for its effectiveness in degrading Reactive red-120 dye. The laccase immobilized biocatalytic CMMs show effective degradation of the Reactive red-120 by 71%, 48%, and 34% at pH 3, 4, and 5, respectively. Furthermore, the immobilized laccase enzyme showed better activity and stability in terms of thermal, pH, and storage compared to the free laccase, leading to increased reusability. The unique combination of Ag NPs and laccase on a thermoresponsive microgel support resulted in a responsive self-cleaning membrane with excellent antimicrobial and dye degradation capabilities for environmentally friendly separation technology.

Iron-rich coal fly ash-polydopamine-silver nanocomposite (IRCFA-PDA-Ag NPs): tailored material for remediation of methylene blue dye from aqueous solution

Water pollution has become one of the most acute environmental problems. One of the pollutants coming to water bodies from industries are dyes, which are harmful to human health, living organisms, and the esthetic appearance of water. Most dyes are toxic, carcinogenic, rarely biodegradable, and highly soluble in water. Therefore, industrial wastewater treatment has become important. Adsorption technique of removal of dyes from water is simple, efficient, and inexpensive as compared to other techniques. Adsorption efficiency depends on the type and surface area of adsorbents. Iron-rich coal fly ash (IRCFA)-Polydopamine (PDA)@ Silver (Ag) nanocomposite was prepared by separating the iron-rich part (IRCFA) from coal fly ash and coated with polydopamine. IRCFA was mixed with 10 mM tris buffer solution containing 1 g dopamine. The prepared IRCFA-PDA was added to an aqueous solution of silver nitrate, heated at 60 °C, and then 30 mL of flower waste extract was added to this solution. Solid IRCFA-PDA@Ag was obtained, and the prepared nanocomposite was used for the removal of methylene blue (MB) dye from water. The nanocomposite used was prepared by a cost-effective method and has high reusability, separability, and fast regeneration ability. The mechanism of removal of MB dye has been discussed in detail.

Rapid degradation of organic pollutants by Fe3O4@PDA/Ag catalyst in advanced oxidation process

Over the past decades, the development of novel catalysts on the degradation of organic pollutants has attracted increasing attention. In this work, we synthesized silver decorated magnetic nanoparticles (Fe₃O₄@PDA/Ag NPs) to activate H₂O₂ for organic pollutants removal via advanced oxidation processes (AOPs). The catalyst was prepared through in-situ reduction of AgNO₃ by the polydopamine (PDA) layer on Fe₃O₄ NPs. Chemiluminescence results obtained from luminol/H₂O₂ system revealed that the catalyst exhibited excellent catalytic effect on the decomposition of H₂O₂ into reactive oxygen species (ROS) and superoxide radical (O₂^-) was mainly responsible for the oxidative degradation. Importantly, the fast evolution frequency of oxygen gas bubbles produced in the reaction of Ag NPs and H₂O₂ could generate vigorous fluid convection and autonomous motion of catalyst when H₂O₂ concentration reached 1%. Additionally, the catalyst can suspend in solution for several minutes. Therefore, by coupling the vigorous motion with slow sedimentation velocity, the catalyst can realize rapid degradation of organic pollutants without external mixing force. The Fe₃O₄@PDA/Ag NPs catalysts not only showed a high removal efficiency of malachite green, but also can be applied for the degradation of other dyes, making it to be a promise candidate for environmental remediation. With the merits of excellent catalytic effect, fast degradation speed, and simplicity of operation, the prepared catalysts exhibits great potential in the practical field.

Decolorization of Rhodamine B by silver nanoparticle-loaded magnetic sporopollenin: characterization and process optimization

Silver nanoparticles (Ag NPs) were reduced on the surface of magnetic sporopollenin (Fe₃O₄@SP) modified with poly-dopamine to enhance the degradation capability for Rhodamine B (RhB). The polydopamine-coated Fe₃O₄@SP (PDA@ Fe₃O₄@SP) acts as a self-reducing agent for Ag⁺ ions to Ag⁰. The structural properties of the synthesized nanocomposite were determined using Fourier transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), and vibrating sample magnetometer (VSM). The systematic study of the degradation process was performed using Response Surface Methodology (RSM) to determine the relationship between the four process variables, namely, initial RhB concentration, NaBH₄ amount, catalyst amount, and time. Optimum points were determined for these four parameters using both matrix and numerical optimization methods. Under optimum conditions, RhB was decolorized with a yield of 98.11%. The apparent activation energy (E_a) and rate constant (k) for the degradation were 24.13 kJ/mol and 0.77 min^-1, respectively. The reusability studies of the Ag@PDA@Fe₃O₄@SP exhibited more than 85% degradation ability of the dye even after five cycles. As a result, Ag@PDA@Fe₃O₄@SP possessed high catalytic activity, fast reduction rate, good reusability, easy separation, and simple preparation, endowing this catalyst to be used as a promising catalyst for the decolorization of dyes in aqueous solutions.

Green-Routed Carbon Dot-Adorned Silver Nanoparticles for the Catalytic Degradation of Organic Dyes

Herein, a simple, cost-effective, and in-situ environmentally friendly approach was adopted to synthesize carbon dot-adorned silver nanoparticles (CDs@AgNPs) from yellow myrobalan (Terminalia chebula) fruit using a hydrothermal treatment without any additional reducing and or stabilizing agents. The as-synthesized CDs@AgNP composite was systematically characterized using multiple analytical techniques: FESEM, TEM, XRD, Raman, ATR-FTIR, XPS, and UV-vis spectroscopy. All the results of the characterization techniques strongly support the idea that the CDs were successfully made to adorn the AgNPs. This effectively synthesized CDs@AgNP composite was applied as a catalyst for the degradation of organic dyes, including methylene blue (MB) and methyl orange (MO). The degradation results revealed that CDs@AgNPs exhibit a superior catalytic activity in the degradation of MB and MO in the presence of NaBH4 (SB) under ambient temperatures. In total, 99.5 and 99.0% rates of degradation of MB and MO were observed using CDs@AgNP composite with SB, respectively. A plausible mechanism for the reductive degradation of MB and MO is discussed in detail. Moreover, the CDs@AgNP composite has great potential for wastewater treatment applications.

Sustainable nanotechnology based wastewater treatment strategies: achievements, challenges and future perspectives

Nanotechnology is being an emerging science for wastewater treatment requires more research emphasis and depth knowledge. For wastewater treatment, different forms of nanomaterials are used based on the type of contaminants and treatment efficiency desired. With the development in the field of nanomaterials, novel and emerging nanomaterials are coming into existence. The nanomaterials used for wastewater treatment can be carbon, single-walled carbon nanotubes, multiple walled carbon nanotubes, covalent organic frameworks, metal and metal oxide- based nanoparticles. Graphene based nanoparticles, their oxides (GO) and reduced graphene oxide (rGO) find tremendous applicability to be used in wastewater treatment purposes. Due to the introduction of graphene oxide nanoparticles in the adsorbent materials, their adsorption capacities have get enhanced and such materials have also improved the mechanical stability of the adsorbent. Ferric oxide shows greater adsorption capacities for organic pollutants. Furthermore, magnetic nano-powder confers a low adsorption capacity for phenols. Pyrrolidone reduced graphene oxide (PVP-RGO) nanoparticles have been used as adsorbents for the elimination of inorganic target contaminant copper, with great adsorption (1698 mg/g). The present study comprehensively reviews nanotechnology as a wastewater treatment strategy besides enlightening its safety issues and efficiency. The novelty of this article is that it highlights the overview of recent applications of various types of nanomaterials and research works releated to it. Such an approach will be helpful to get insights into technological advances, applications and future challenges of nanotechnology implementation for wastewater treatment.

Novel pathway for the sonochemical synthesis of silver nanoparticles with near-spherical shape and high stability in aqueous media

The present study shows the development of a novel sonochemical synthesis pathway of sub-15 nm silver nanoparticles (AgNPs) with quasi-spherical shape and high stability in aqueous suspension. Different analytical techniques such as on-line UV-Vis spectroscopy, Atomic Force Microscopy (AFM), and Transmission Electron Microscopy (TEM) were complementarily used to characterize the evolution of the properties of AgNPs synthesized with this new route. Furthermore, different centrifugation conditions were studied to establish a practical, simple and straightforward purification method. Particle size was determined by TEM employing two different deposition methods, showing that purified AgNPs have a size of 8.1 nm ± 2.4 nm with a narrow dispersion of the size distribution (95% coverage interval from 3.4 to 13 nm). Critical information of the shape and crystalline structure of these sub-15 nm AgNPs, provided by shape descriptors (circularity and roundness) using TEM and high resolution (HR)-TEM measurements, confirmed the generation of AgNPs with quasi-spherical shapes with certain twin-fault particles promoted by the high energy of the ultrasonic treatment. Elemental analysis by TEM-EDS confirmed the high purity of the sub-15 nm AgNPs, consisting solely of Ag. At the optical level, these AgNPs showed a bandgap energy of (2.795 ± 0.002) eV. Finally, the evaluation of the effects of ultraviolet radiation (UVC: 254 nm and UVA: 365 nm) and storage temperature on the spectral stability revealed high stability of the optical properties and subsequently dimensional properties of sub-15 nm AgNPs in the short-term (600 min) and long-term (24 weeks).

Polydopamine Functionalized Graphene Oxide as Membrane Nanofiller: Spectral and Structural Studies

High-degree functionalization of graphene oxide (GO) nanoparticles (NPs) using polydopamine (PDA) was conducted to produce polydopamine functionalized graphene oxide nanoparticles (GO-PDA NPs). Aiming to explore their potential use as nanofiller in membrane separation processes, the spectral and structural properties of GO-PDA NPs were comprehensively analyzed. GO NPs were first prepared by the oxidation of graphite via a modified Hummers method. The obtained GO NPs were then functionalized with PDA using a GO:PDA ratio of 1:2 to obtain highly aminated GO NPs. The structural change was evaluated using XRD, FTIR-UATR, Raman spectroscopy, SEM and TEM. Several bands have emerged in the FTIR spectra of GO-PDA attributed to the amine groups of PDA confirming the high functionalization degree of GO NPs. Raman spectra and XRD patterns showed different crystalline structures and defects and higher interlayer spacing of GO-PDA. The change in elemental compositions was confirmed by XPS and CHNSO elemental analysis and showed an emerging N 1s core-level in the GO-PDA survey spectra corresponding to the amine groups of PDA. GO-PDA NPs showed better dispersibility in polar and nonpolar solvents expanding their potential utilization for different purposes. Furthermore, GO and GO-PDA-coated membranes were prepared via pressure-assisted self-assembly technique (PAS) using low concentrations of NPs (1 wt. %). Contact angle measurements showed excellent hydrophilic properties of GO-PDA with an average contact angle of (27.8°).

Emerging nano-structured innovative materials as adsorbents in wastewater treatment

Water supply around the globe is struggling to meet the rapidly increasing demand by the population, drastic changes in climate and degrading water quality. Even though, many large-scale methods are employed for wastewater treatment they display several negative impacts owing to the presence of pollutants. Technological innovation is required for integrated water management with different groups of nanomaterials for the removal of toxic metal ions, microbial disease, organic and inorganic solutes. The method of manipulating atoms on a nanoscale is nanotechnology. Nanomembranes are used in nanotechnology to soften water and eliminate physical, chemical and biological pollutants. The present review concentrates on various nanotechnological approaches in wastewater remedy, mechanisms involved to promote implementation, benefits and limitations in comparison with current processes, properties, barriers and commercialization research needs. Also the review identifies opportunities for further exploiting the exclusive features for green water management by following the advances in nanotechnology.

Beta-Cyclodextrin-Assisted Synthesis of Silver Nanoparticle Network and Its Application in a Hydrogen Generation Reaction

The unsustainable nature of carbon-based fuels has prompted scientists and engineers to investigate alternative sources of energy. Silver nanoparticle networks (AgNPNs) were synthesized using beta-cyclodextrin for applications in hydrogen evolution reactions from sodium borohydride (NaBH4). The identities of the AgNPNs were confirmed using ultraviolet–visible spectroscopy, X-ray diffraction, and Transmission electron microscopy (TEM). The catalytic activity of the hydrogen evolution reactions was measured using a gravimetric water displacement system. The data collected show an increase in the efficiency of the hydrogen generation reaction with the addition of AgNPN. The silver nanoparticle network catalyst performed best at 22 °C with an increased concentration of NaBH4 producing hydrogen at a rate of 0.961 mL∙min−1∙mLcat−1. The activation energy was calculated to be 50.3 kJ/mol.