Remediation of pharmacophoric laboratory waste by using biodegradable carbon nanoparticles of bacterial biofilm origin

Research laboratories generate a broad range of hazardous pharmacophoric chemical contaminants, from drugs to dyes used during various experimental procedures. In the recent past, biological methods have demonstrated great potential in the remediation of such contaminants. However, the presence of pharmacophoric chemicals containing antibiotics, xenobiotics, and heavy metals suppresses the growth and survivability of used microbial agents, thus decreasing the overall efficiency of biological remediation processes. Bacterial biofilm is a natural arrangement to counter some of these inhibitions but its use in a systemic manner, portable devices, and pollutant remediation plants post serious challenges. This could be countered by synthesizing a biodegradable carbon nanoparticle from bacterial biofilm. In this study, extracellular polymeric substance-based carbon nanoparticles (Bio-EPS-CNPs) were synthesized from bacterial biofilm derived from Bacillus subtilis NCIB 3610, as a model bacterial system. The produced Bio-EPS-CNPs were investigated for physiochemical properties by dynamic light scattering, optical, Fourier-transformed infrared, and Raman spectroscopy techniques, whereas X-ray diffraction study, scanning electron microscopy, and transmission electron microscopy were used to investigate structural and morphological features. The Bio-EPS-CNPs exhibited negative surface charge with spherical morphology having a uniform size of sub-100 nm. The maximum remediation of some laboratory-produced pharmacophoric chemicals was achieved through a five-round scavenging process and confirmed by UV/Vis spectroscopic analysis with respect to the used pharmacophore. This bioinspired remediation of used pharmacophoric chemicals was achieved through the mechanism of surface adsorption via hydrogen bonding and electrostatic interactions, as revealed by different characterizations. Further experiments were performed to investigate the effects of pH, temperature, stirring, and the protocol of scavenging to establish Bio-EPS-CNP as a possible alternative to be used in research laboratories for efficient removal of pharmacophoric chemicals by incorporating it in a portable, filter-based device.

Role of transition metals in coinage metal nanoclusters for the remediation of toxic dyes in aqueous systems

A difficult issue in chemistry and materials science is to create metal compounds with well-defined components. Metal nanoclusters, particularly those of coinage groups (Cu, Ag, and Au), have received considerable research interest in recent years owing to the availability of atomic-level precision via joint experimental and theoretical methods, thus revealing the mechanisms in diverse nano-catalysts and functional materials. The textile sector significantly contributes to wastewater containing pollutants such as dyes and chemical substances. Textile and fabric manufacturing account for about 7 × 105 tons of wastewater annually. Approximately one thousand tons of dyes used in textile processing and finishing has been recorded as being discharged into natural streams and water bodies. Owing to the widespread environmental concerns, research has been conducted to develop absorbents that are capable of removing contaminants and heavy metals from water bodies using low-cost technology. Considering this idea, we reviewed coinage metal nanoclusters for azo and cationic dye degradation. Fluorometric and colorimetric techniques are used for dye degradation using coinage metal nanoclusters. Few reports are available on dye degradation using silver nanoclusters; and some of them are discussed in detailed herein to demonstrate the synergistic effect of gold and silver in dye degradation. Mostly, the Rhodamine B dye is degraded using coinage metals. Silver nanoclusters take less time for degradation than gold and copper nanoclusters. Mostly, H2O2 is used for degradation in gold nanoclusters. Still, all coinage metal nanoclusters have been used for the degradation due to suitable HOMO-LUMO gap, and the adsorption of a dye onto the surface of the catalyst results in the exchange of electrons and holes, which leads to the oxidation and reduction of the adsorbed dye molecule. Compared to other coinage metal nanoclusters, Ag/g-C3N4 nanoclusters displayed an excellent degradation rate constant with the dye Rhodamine B (0.0332 min-1). The behavior of doping transition metals in coinage metal nanoclusters is also reviewed herein. In addition, we discuss the mechanistic grounds for degradation, the fate of metal nanoclusters, anti-bacterial activity of nanoclusters, toxicity of dyes, and sensing of dyes.

Utilizing Cymbopogon Proximus Grass Extract for Green Synthesis of Zinc Oxide Nanorod Needles in Dye Degradation Studies

This study successfully synthesized zinc oxide nanorod needles (ZnO-NRNs) using an environmentally friendly method employing Cymbopogon Proximus extract. The resulting ZnO-NRNs exhibited exceptional physicochemical and structural properties, confirmed through various characterization techniques, including UV-Vis spectrophotometry, dynamic light scattering (DLS), transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX). The analysis revealed a hexagonal wurtzite structure with high crystallinity, a 3.6 eV band gap, and a notably blue-shifted absorption band. ZnO-NRNs showed impressive photocatalytic activity, degrading Rhodamine B dye by 97% under UV and visible sunlight, highlighting their photostability and reusability. This green synthesis process offers cost effectiveness and environmental sustainability for practical applications.

Antimicrobial efficacy of Mentha piperata-derived biogenic zinc oxide nanoparticles against UTI-resistant pathogens

Misuse of antibiotics leads to the worldwide spread of antibiotic resistance, which motivates scientists to create new antibiotics. The recurring UTI due to antibiotics-resistant microorganism's challenges scientists globally. The biogenic nanoparticles have the potential to meet the escalating requirements of novel antimicrobial agents. The green synthesis of nanoparticles (NPs) gained more attention due to their reliable applications against resistant microbes. The current study evaluates the biogenic ZnO NPs of Mentha piperata extract against resistant pathogens of urinary tract infections by agar well diffusion assay. The biogenic ZnO NPs revealed comparatively maximum inhibition in comparison to synthetic antibiotics against two bacterial strains (Proteus mirabilis, Pseudomonas aeruginosa) and a fungal strain (Candida albicans).The synthesized biogenic ZnO NPs alone revealed maximum activities than the combination of plant extract (PE) and ZnO NPs, and PE alone. The physiochemical features of ZnO NPs characterized through UV-Vis spectroscopy, FTIR, XRD, SEM, and EDX. The UV-Vis spectroscopy revealed 281.85 nm wavelengths; the XRD pattern revealed the crystalline structure of ZnO NPs. The FTIR analysis revealed the presence of carboxylic and nitro groups, which could be attributed to plant extract. SEM analysis revealed spherical hollow symmetry due to electrostatic forces. The analysis via EDX confirmed the presence of Zn and oxygen in the sample. The physiochemical features of synthesized ZnO NPs provide pivotal information such as quality and effectiveness. The current study revealed excellent dose-dependent antimicrobial activity against the pathogenic isolates from UTI-resistant patients. The higher concentration of ZnONPs interacts with the cell membrane which triggers oxidative burst. They may bind with the enzymes and proteins and brings epigenetic alteration which leads to membrane disruption or cell death.

Exploring the potential of ZnO-Ag@AgBr/SBA-15 Z-scheme heterostructure for efficient wastewater treatment: synthesis, characterization, and real-world applications

This study reports on the synthesis and characterization of ZnO-Ag@AgBr/SBA-15 composites using natural halloysite clay from Yenbai Province, Vietnam, as a silica aluminum source. The synthesized materials demonstrated visible light absorption with a band gap energy range of 2.63-2.98 eV. The dual Z-scheme ZnO-Ag@AgBr/SBA-15 heterojunction exhibited superior catalytic performance compared to ZnO/SBA-15 and Ag@AgBr/SBA-15, owing to its improved electron transfer and reduced electron and hole recombination rate. In particular, the photocatalytic efficiency of ZnO-Ag@AgBr/SBA-15 was evaluated for the removal of harmful phenol red from wastewater under visible light irradiation. The photocatalytic process was optimized by varying the phenol red concentration, pH, and catalyst dosage, and showed that 98.8% of phenol red in 100 mL wastewater (pH = 5.5) can be removed using 40 mg of 20%ZnO-Ag@AgBr/SBA-15 within 120 min. Furthermore, the degradation pathway of phenol red was predicted using liquid chromatographic-mass spectrometry (LC-MS). Finally, the photocatalytic process was successfully tested using water samples collected from the four main domestic waste sources in Hanoi, including the To Lich River, the Hong River, the Hoan Kiem Lake, and the West Lake, demonstrating the high potential of the ZnO-Ag@AgBr/SBA-15 photocatalyst for phenol red degradation in real-world wastewater treatment applications.

Comparative Reactive Blue 4 Dye Removal by Lemon Peel Bead Doping with Iron(III) Oxide-Hydroxide and Zinc Oxide

The increasing concern of dye contamination in wastewater results in the toxicity of aquatic life and water quality, so wastewater treatment is required to treat the low water quality standard for safety purposes. Lemon peel beads-doped iron(III) oxide-hydroxide (LBF) and lemon peel beads-doped zinc oxide (LBZ) were synthesized and characterized to investigate their crystalline structure, surface morphology, chemical compositions, chemical functional groups, and ζ potentials by X-ray diffraction, field emission scanning electron microscopy and focused ion beam, energy dispersive X-ray spectroscopy, Fourier transform infrared, and zetasizer techniques. Their effects of dose, contact time, temperature, pH, and concentration for reactive blue 4 (RB4) dye removal efficiencies were investigated by batch experiments, and their adsorption isotherms, kinetics, and desorption experiments were also studied. LBF and LBZ demonstrated semicrystalline structures, and their surface morphologies had a spherical shape with coarse surfaces. Five main elements of carbon (C), oxygen (O), calcium (Ca), chlorine (Cl), and sodium (Na) and six main function groups of O-H, C≡N, C=C, C-OH, C-O-C, and C-H were detected in both materials. The results of ζ potential demonstrated that both LBF and LBZ had negative charges on the surface at all pH values, and their surfaces increased more of the negative charge with the addition of the pH value from 2-12. For batch tests, the RB4 dye removal efficiencies of LBF and LBZ were 83.55 and 66.64%, respectively, so LBF demonstrated a higher RB4 dye removal efficiency than LBZ. As a result, the addition of iron(III) oxide-hydroxide helped in improving the material efficiency more than zinc oxide. In addition, both LBF and LBZ could be reused in more than five cycles for RB4 dye removal of more than 41%. The Freundlich model was a good explanation for their adsorption patterns relating to physiochemical adsorption, and a pseudo-second-order kinetic model was a well-fitted model for explaining their adsorption mechanism correlating to the chemisorption process with heterogeneous adsorption. Therefore, LBF was a potential adsorbent to further apply for RB4 dye removal in industrial applications.

Chitosan IR806 dye-based polyelectrolyte complex nanoparticles with mitoxantrone combination for effective chemo-photothermal therapy of metastatic triple-negative breast cancer

Chemo-photothermal therapy is one of the emerging therapies for treating triple-negative breast cancer. In this study, we have used ionotropic gelation method to fabricate chitosan and IR806 dye-based polyelectrolyte complex (CIR-PEx) nanoparticles. These nano-complexes were in size range of 125 ± 20 nm. The complexation of IR 806 dye with chitosan improved photostability, photothermal transduction, and showed excellent biocompatibility. Cancer cells treated with CIR-PEx NPs enhanced intracellular uptake within 5 h of incubation and also displayed mitochondrial localization. With the combination of CIR-PEx NPs and a chemotherapeutic agent (i.e., mitoxantrone, MTX), a significant decline in cancer cell viability was observed in both 2D and 3D cell culture models. The chemo-photothermal effect of CIR-PEx NPs + MTX augmented apoptosis in cancer cells when irradiated with NIR light. Furthermore, when tested in the 4 T1-tumor model, the chemo-photothermal therapy showed a drastic decline in tumor volume and inhibited metastatic lung nodules. The localized hyperthermia caused by photothermal therapy reduced the primary tumor burden, and the chemotherapeutic activity of mitoxantrone further complemented by inhibiting the spread of cancer cells. The proposed chemo-photothermal therapy combination could be a promising strategy for treating triple-negative metastatic breast cancer.

Insights into ZnO-based doped porous nanocrystal frameworks

Colloidal nanocrystals play a vital role in several applications. The doping of cations in the nanocrystal matrix enhances the optical, electrical, and magnetic properties. The number and well-defined distribution of the dopant are crucial to protect the nanocrystal from clustering. The XRD, XPS, and XAS instruments reveal the change in the lattice parameters, chemical states, and local coordination environment information. In addition of detecting the position and distribution of the dopant, the 4D-STEM detector mode gathers all types of real-space atomic-resolution images by collecting all diffraction datasets from each electron probe with high-speed and efficient detection. Dopant-host ligand type, reactions conditions, and reaction time optimization during synthesis are critical for the host and dopant reactivity balance. Pearson's hard/soft acids/bases theory would be a base for balancing the solubility of the dopant-host in the given solvents/surfactant. In addition, tuning the colloidal nanocrystals to secondary structures, which enhances the mass-/ions transport, can contribute a combination of properties that do not exist in the original constituents.

Insight into nanocrystal synthesis: from precursor decomposition to combustion

Nanotechnology-based synthesis of nanoscale materials has appealed to the attention of scientists in the modern scientific community. In the bottom-up approach, atoms start to aggregate/agglomerate and form nuclei within the minimum and maximum supersaturation range. Once nuclei are generated above the critical-free energy/radius, the growth is initiated by obeying the LaMar model with a slight extra simple growth by diffusion advancement. The in situ real-time liquid phase analysis using STEM, AFM, and XAS techniques is used to control precursor decomposition to the nanocrystal formation process and should be a non-stoppable technique. Solution combustion synthesis (SCS) is a time-/energy-efficient self-sustained process that produces mass-/ion transport active porous materials. SCS also permits the synthesis of evenly distributed-doped and hybrid-nanomaterials, which are beneficial in tuning crucial properties of the materials. The growth and development of nanocrystals, dehydrating the sol in the presence of a surfactant or/and fuel results in combustion once it arrives at the ignition temperature. Besides, the kinetic and thermodynamics controlled architecture-directing agent-assisted SCS offers colloidal nanocrystal framework formation, which is currently highly applicable for energy devices. This short review provides insightful information that adds to the existing nanocrystal synthesis process and solution combustion synthesis and recommends future directions in the field.

The LaMar model visualizes the process of nanocrystal formation. The solution combustion synthesis approach is a noble methodology resulting in highly stable and ordered porous nanomaterials.

Green synthesis strategy for producing doped and undoped ZnO nanoparticles: their photocatalytic studies for industrial dye degradation

A facile and green method for synthesizing Zinc Oxide nanoparticles (ZnO NPs) was successfully carried out using unutilized sweet lime; i.e., Citrus Limetta rind pulp (U-CLRP) extract. The structural, morphological and optical studies were elucidated to confirm the crystallinity, size, and shape of the synthesized NPs. Copper doping on ZnO NPs (CZnO NPs) was carried out to enhance the optical properties. The as-prepared and doped nanoparticle's potential for efficient degradation of a commercial dye, Methylene Blue (MB), was tested under Ultraviolet (UV) and visible light radiation. ZnO NPs showed promising results for dye degradation while an improved result was witnessed for CZnO NPs. ZnO NPs showed 74% of degradation of MB dye under UV irradiation and 57% degradation under visible light radiation. CZnO NPs presented 85 and 90% degradation in the UV and visible radiation, respectively. This green reduction method utilizing biological waste sources shows a promising path for photocatalysts to be developed economically as well as efficiently in the future. These CZnO/ ZnO NPs proved their potential for embedding them as efficient catalysts for wastewater treatment plants of textile industries.

Micro-Plasma Assisted Synthesis of ZnO Nanosheets for the Efficient Removal of Cr6+ from the Aqueous Solution

Herein, we report a micro-plasma assisted solvothermal synthesis and characterization of zinc oxide nanosheets (ZnO-NSs) and their application for the removal of Cr6+ ion from aqueous solution. The morphological investigations by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the high-density growth of nanosheets with the typical sizes in the range of 145.8–320.25 nm. The typical surface area of the synthesized ZnO-NSs, observed by Brunauer-Emmett-Teller (BET), was found to be 948 m2/g. The synthesized ZnO-NSs were used as efficient absorbent for the removal of Cr6+ ion from aqueous solution. Various parameters such as pH, contact time, amount of adsorbate and adsorbent on the removal efficiency of Cr6+ ion was optimized and presented in this paper. At optimized conditions, the highest value for removal was 87.1% at pH = 2 while the calculated maximum adsorption capacity was ~87.37 mg/g. The adsorption isotherm data were found to be best fitted to Temkin adsorption isotherm and the adsorption process followed the pseudo-first-order kinetics. Furthermore, the toxicity of ZnO-NSs were also examined against fibroblast cells, which show favorable results and proved that it can be used for wastewater treatment.

Electrical behavior and enhanced photocatalytic activity of (Ag, Ni) co-doped ZnO nanoparticles synthesized from co-precipitation technique

Methylene blue (MB) dye is the most common harmful, toxic, and non-biodegradable effluent produced by the textile industries. The present study investigates the effect of zinc oxide (ZnO) nanoparticles (NPs) and Ag-Ni doped ZnO NPs on the performance of photocatalytic degradation of MB dye. Pure ZnO and Ag-Ni doped ZnO NPs are synthesized using the co-precipitation method. The crystalline nature and surface morphology of the synthesized pure ZnO and Ag-Ni doped ZnO NPs was characterized by powder X-ray diffraction, scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM) analysis. The presence of spherical-like morphologies was confirmed from SEM and HRTEM analysis. The presence of Ni-O and Zn-O bands in the synthesized materials was found by Fourier transform infrared (FTIR) spectroscopy analysis. The MB dye was degraded under UV-light exposure in various pH conditions. The Ag (0.02%)-Ni doped ZnO NPs exhibits highest photocatalytic activity of 77% under pH 4.

Efficient deoxygenation of waste cooking oil over Co3O4–La2O3-doped activated carbon for the production of diesel-like fuel

Untreated waste cooking oil (WCO) with significant levels of water and fatty acids (FFAs) was deoxygenated over Co₃O₄–La₂O₃/AC_nano catalysts under an inert flow of N₂ in a micro-batch closed system for the production of green diesel.

ZnO (Ag-N) Nanorods Films Optimized for Photocatalytic Water Purification

ZnO nanorods (NRs) films, nitrogen-doped (ZnO:N), and ZnO doped with nitrogen and decorated with silver nanostructures (ZnO:N-Ag) NRs films were vertically supported on undoped and N doped ZnO seed layers by a wet chemical method. The obtained films were characterized structurally by X-ray diffraction. Morphological and elemental analysis was performed by scanning electron microscopy, including an energy dispersive X-ray spectroscopy facility and their optical properties by Ultraviolet-Visible Spectroscopy. Analysis performed in the NRs films showed that the nitrogen content in the seed layer strongly affected their structure and morphology. The mean diameter of ZnO NRs ranged from 70 to 190 nm. As the nitrogen content in the seed layer increased, the mean diameter of ZnO:N NRs increased from 132 to 250 nm and the diameter dispersion decreased. This diameter increase occurs simultaneously with the incorporation of nitrogen into the ZnO crystal lattice and the increase in the volume of the unit cell, calculated using the X-ray diffraction patterns and confirmed by a slight shift in the XRD angle. The diffractograms indicated that the NRs have a hexagonal wurtzite structure, with preferential growth direction along the c axis. The SEM images confirmed the presence of metallic silver in the form of nanoparticles dispersed on the NRs films. Finally, the degradation of methyl orange (MO) in an aqueous solution was studied by UV-vis irradiation of NRs films contained in the bulk of aqueous MO solutions. We found a significant enhancement of the photocatalytic degradation efficiency, with ZnO:N-Ag NRs film being more efficient than ZnO:N NRs film, and the latter better than the ZnO NRs film.

Enhanced dye removal using polymeric nanocomposite through incorporation of Ag doped ZnO nanoparticles: Synthesis and characterization

A facile method was approached to synthesize a new series of highly porous polyethylene glycol (PEG) and Ag-ZnO (AZO) grafted polyaniline (PANI) nanocomposites (PAPE/AZO) for investigation of the adsorption behavior of brilliant green dye (BG). The compositions of Ag (1, 3 and 5%) in AZO were varied to assess the influence of bimetallic oxide incorporation. The nanocomposites were characterized by FTIR, XRD, SEM and TEM analyses. The adsorption performance of the PAPE/AZO was assessed by various parametric changes viz. contact time, pH, temperature, concentration of the dye and adsorbent dosage. The highest adsorption capacity of 94.46 mg g^-1 was achieved at the optimum conditions of 0.075 g adsorbent dosage, 70 mg L^-1 dye concentration, 1% AZO and pH 2. BET and BJH analyses of the nanocomposite confirmed the higher surface area and pore volume with lower amount of AZO that supported PAPE for enhanced dye removal. The Langmuir isotherm model fits the equilibrium conditions indicating a homogeneous distribution of active sites on the surface of the nanocomposite. Adsorption kinetic model ensued pseudo second order exhibiting chemisorption process. From the results, it is obvious that PAPE/AZO can be used as a potential core substance for treating real-time industrial dye effluents.

Translucent Photodetector with Blended Nanowires-Metal Oxide Transparent Selective Electrode Utilizing Photovoltaic and Pyro-Phototronic Coupling Effect

ZnO is a potential candidate for photodetection utilizing the pyroelectric effect. Here, a self-biased and translucent photodetector with the configuration of Cu₄ O₃ /ZnO/FTO/Glass is designed and fabricated. In addition, the pyroelectric effect is effectively harvested using indium tin oxide (ITO), silver nanowires (AgNWs), and a blend of AgNWs-coated ITO as the transparent selective contact electrode. The improved rise times are observed from 1400 µs (bare condition; without the selective electrode) to 69, 60, 7 µs, and fall times from 720 µs (bare condition) to 80, 70, 10 µs for corresponding ITO, AgNWs, and AgNWs-coated ITO contact electrodes, respectively. Similarly, the responsivity and detectivity are enhanced by about 4.39 × 10⁷ and 5.27 × 10⁵ %, respectively. An energy band diagram is proposed to explain the underlying working mechanism based on the workfunction of the ITO (4.7 eV) and AgNWs (4.57 eV) as measured by Kelvin probe force microscopy, which confirms the formation of type-II band alignment resulting in the efficient transport of photogenerated charge carriers. The functional use of the transparent selective contact electrode can effectively harness the pyro-phototronic effect for next-generation transparent and flexible optoelectronic applications.

Ag-doped ZnO nanorods embedded reduced graphene oxide nanocomposite for photo-electrochemical applications

In this paper, the Ag-doped zinc oxide nanorods embedded reduced graphene oxide (ZnO:Ag/rGO) nanocomposite was synthesized for photocatalytic degradation of methyl orange (MO) in the water. The microstructural results confirmed the successful decoration of Ag-doped ZnO nanorods on rGO matrix. The photocatalytic properties, including photocatalytic degradation, charge transfer kinetics and photocurrent generation, are systematically investigated using electrochemical impedance spectroscopy (EIS), photocurrent transient response (PCTR) and open circuit voltage decay (OCVD). The results of photocatalytic dye degradation measurements indicated that ZnO:Ag/rGO nanocomposite is more effective than pristine ZnO to degrade the MO dye, and the degradation rate reached 40.6% in 30 min. The decomposition of MO with ZnO:Ag/rGO nanostructure followed first-order reaction kinetics with a reaction rate constant (K a) of 0.01746 min-1. The EIS, PCTR and OCVD measurements revealed that the Ag doping and incorporation of rGO could suppress the recombination probability in ZnO by the separation of photo-generated electron-hole pairs, which leads to the enhanced photocurrent generation and photocatalytic activity. The photocurrent density of ZnO:Ag/rGO, ZnO/rGO and pristine ZnO are 206, 121.4 and 88.8 nA cm-2, respectively.

Concurrent biomineralization of silver ions into Ag0 and AgxO by Leptolyngbya strain JSC-1 and the establishment of its axenic culture

Ionic silver is a potential hazard to aquatic life forms because of the increasing usage of silver based materials. The need for developing a sustainable and ecofriendly process to minimize the toxic effects of the free ions burden is now a scientific consensus. Therefore, we report the latest results in cyanobacterium Leptolyngbya JSC-1 investigating the tolerance towards toxic doses of silver, its extracellular biomineralization and silver nano-deposits formation inside the cells, and speculate about potential environmental impacts. In this study, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) analysis reveal the extracellular biomineralization of soluble silver (1-100 μM) into corresponding nanoparticles (50-100 nm in diameter) by JSC-1, while X-ray photoelectron spectroscopy (XPS) examination divulged the presence of both Ag⁺ and Ag⁰ in extracellularly biomineralized silver, depicting a mixture of both Ag_xO and elemental Ag. The scanning transmission electron microscopy (STEM), EDS and elemental mapping visualized the formation of intracellular silver nanoparticles. Moreover, this feature of silver tolerance in JSC-1 was further exploited and a novel protocol was developed for isolation and maintenance of axenic culture of this filamentous cyanobacterium. Consequently, this capability of silver biomineralization by JSC-1, both extra- and intra-cellularly might be useful for modeling the Ag resistance mechanism in cyanobacteria and also might be a sustainable alternative for heavy metals bioremediation in aquatic environments.

Free-standing red phosphorous/silver sponge monolith as an efficient and easily recyclable macroscale photocatalyst for organic pollutant degradation under visible light irradiation

Traditional nano-sized photocatalysts in powdery form suffer from difficulties in recyclability, and have to be immobilized before practical applications. In this study, red phosphorous/silver (red P/Ag) sponge monolith was discovered to be a new free-standing macroscale photocatalyst, which was fabricated by a one-pot hydrothermal method without using any organic surfactants or templates for the first time. The elemental red P not only functioned as a reducing agent in the formation of Ag sponge monolith during the synthesis processes, but also as the active photocatalyst in-situ immobilized onto the Ag sponge. The as-prepared red P/Ag sponge monolith showed enhanced photocatalytic activity than that of traditional pure powdery red P by a factor of 3.1 times for organic pollutants (i.e. Rhodamine 6G, phenol) degradation under visible light irradiation. The enhancement was mainly attributed to the function of Ag sponge served as good electron sink to trap photo-generated electrons. More importantly, such free-standing macroscale photocatalyst can be easily recycled without activity deterioration. As a proof of concept, this work provides new insights into not only for the development of red P-based elemental photocatalysts, but also for the one-pot fabrication of novel free-standing macroscale materials with excellent photocatalytic activity for practical environmental applications.

Flexible resistive switching bistable memory devices using ZnO nanoparticles embedded in polyvinyl alcohol (PVA) matrix and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)

The resistive switching memory effects in metal-insulator-metal devices with aluminium (Al) as top electrode (TE) and bottom electrode (BE). A solution processed active layer consisting of zinc oxide (ZnO) nanoparticles embedded in an insulating polyvinyl alcohol (PVA) matrix and polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has been studied by using flexible polyethylene terephthalate (PET) substrates. The current–voltage (I–V) measurements of hybrid Al/ZnO–PVA/PEDOT:PSS/Al/flexible PET substrate device exhibited a non-volatile bistable resistive switching behaviour, which is attributed to the trapping, storage and transport of charges in the electronic states of the ZnO nanoparticles. The performance of hybrid device is significantly enhanced over control Al/PEDOT:PSS/Al and Al/ZnO–PVA/Al devices due the presence of PEDOT:PSS polymer. This PEDOT:PSS improves the performance of oxygen ions (holes) migration toward BE and protect back oxygen vacancies (electrons) migrate toward BE from ZnO–PVA composites which may reduces the leakage current, as a result, increased the ‘ON state/OFF state’ current ratio of 7.9 × 10³ times. The fabricated hybrid device showed high ON/OFF switching current ratio larger than five orders of magnitude with low operating voltages. It is observed that, the existence of two conducting states, namely, low conductivity state (OFF state) and high conductivity state (ON state), exhibiting bistable behaviour. The state of the device was maintained even after removal of the applied bias, indicating the non-volatile memory. The observed current–time response showed good memory retention behaviour of the fabricated devices. The excellent stability and retention performances of hybrid device verify the reliability of this device and demonstrate their potential for application in non-volatile bistable memory device. The carrier transport mechanism of the bistable behaviour for the fabricated non-volatile organic bistable devices structures is described on the basis of the I–V experimental results by analyzing the effect of space charge and electronic structure. Interestingly, the device performance was not degraded and remains identical even after bending the device from 60–120° angles, which indicates high potential for flexible non-volatile bistable memory device applications. This demonstration provides a class of memory devices with the potential for future flexible electronics applications.

The results clearly show that there was no detectable change in resistive switching characteristics of non-volatile bistable memory device even after bending the device at different angles, making it compatible with flexible electronics.

Disinfection of water with new chitosan-modified hybrid clay composite adsorbent

Hybrid clay composites were prepared from Kaolinite clay and Carica papaya seeds via modification with chitosan, Alum, NaOH, and ZnCl₂ in different ratios, using solvothermal and surface modification techniques. Several composite adsorbents were prepared, and the most efficient of them for the removal of gram negative enteric bacteria was the hybrid clay composite that was surface-modified with chitosan, Ch-nHYCA_1:5 (Chitosan: nHYCA = 1:5). This composite adsorbent had a maximum adsorption removal value of 4.07 × 10⁶ cfu/mL for V. cholerae after 120 min, 1.95 × 10⁶ cfu/mL for E. coli after ∼180 min and 3.25 × 10⁶ cfu/mL for S. typhi after 270 min. The Brouers-Sotolongo model was found to better predict the maximum adsorption capacity (q_max) of Ch-nHYCA_1:5 composite adsorbent for the removal of E. coli with a q_max of 103.07 mg/g (7.93 × 10⁷ cfu/mL) and V. cholerae with a q_max of 154.18 mg/g (1.19 × 10⁸ cfu/mL) while the Sips model best described S. typhi adsorption by Ch-nHYCA_1:5 composite with an estimated q_max of 83.65 mg/g (6.43 × 10⁷ cfu/mL). These efficiencies do far exceed the alert/action levels of ca. 500 cfu/mL in drinking water for these bacteria. The simplicity of the composite preparation process and the availability of raw materials used for its preparation underscore the potential of this low-cost chitosan-modified composite adsorbent (Ch-nHYCA_1:5) for water treatment.

Enhancing the removal of methylene blue by modified ZnO nanoparticles: kinetics and equilibrium studies

This research aims to use modified ZnO nanoparticles to enhance the removal rate of the methylene blue (MB) dye. ZnO nanoparticles are modified by coating their surface with Congo red (CR) dye, henceforth referred to as ZnO/CR. This process is used to produce a Lewis acid on the surface of ZnO to attract any Lewis base such as a MB dye (MB+). Therefore, the stability of ZnO/CR improved, and it resists the change in pH value (from 3 to 9). Several analysis techniques such as scanning electron microscopy, X-ray diffraction, FTIR, and BET method were used to characterize ZnO/CR. Nonlinear and linear regressions of pseudo first-order, pseudo second-order, and Elovich models were used to calculate the kinetic parameters of the adsorption process. The best-fit kinetic equation was investigated using three functions of error analysis: the sum of the squares of the errors, chi-square analysis, and the coefficient of determination. The intraparticle diffusion equation was used to study the diffusion process. The adsorption process of the MB followed the Langmuir model with a maximum capacity (qm) value of 43.5 mg/g. This value is six times greater than the value calculated with pure ZnO. Thermodynamic parameters ΔS•, ΔH•, and ΔG• were investigated at four temperatures (10, 20, 30, and 40 °C). The uptake process of the MB occurs spontaneously following endothermic process and an increase in the system disorder. The rate of adsorption was controlled mainly by a Lewis acid–base interaction and H bonding. Furthermore, the removal of the MB by ZnO/CR powder worked well as a chemical and physical adsorption process.

Nanostructured ZnO-TiO2 thin film oxide as anode material in electrooxidation of organic pollutants. Application to the removal of dye Amido black 10B from water

Electrochemical oxidative degradation of diazo dye Amido black 10B (AB10B) as model pollutant in water has been studied using nanostructured ZnO-TiO₂ thin films deposited on graphite felt (GrF) substrate as anode. The influence of various operating parameters, namely the current intensity, the nature and concentration of catalyst, the nature of electrode materials (anode/cathode), and the adsorption of dye and ambient light were investigated. It was found that the oxidative degradation of AB10B followed pseudo first-order kinetics. The optimal operating conditions for the degradation of 0.12 mM (74 mg L^-1) dye concentration and mineralization of its aqueous solution were determined as GrF-ZnO-TiO₂ thin film anode, 100 mA current intensity, and 0.1 mM Fe²⁺ (catalyst) concentration. Under these operating conditions, discoloration of AB10B solution was reached at 60 min while 6 h treatment needed for a mineralization degree of 91 %. Therefore, this study confirmed that the electrochemical process is effective for the degradation of AB10B in water using nanostructured ZnO-TiO₂ thin film anodes.

Sol-gel synthesis of thorn-like ZnO nanoparticles endorsing mechanical stirring effect and their antimicrobial activities: Potential role as nano-antibiotics

The effect of mechanical stirring on sol-gel synthesis of thorn-like ZnO nanoparticles (ZnO-NPs) and antimicrobial activities is successfully reported in this study. The in-house synthesized nanoparticles were characterized by XRD, SEM, TEM, FTIR, TGA, DSC and UV-visible spectroscopy. The X-Ray Diffraction analysis revealed the wurtzite crystal lattice for ZnO-NPs with no impurities present. The diametric measurements of the synthesized thorn-like ZnO-NPs (morphology assessed by SEM) were well accounted to be less than 50 nm with the help of TEM. Relative decrease in aspect ratio was observed on increasing the agitation speed. The UV-visible spectroscopy showed the absorption peaks of the ZnO-NPs existed in both UVA and UVB region. A hypsochromic shift in λmax was observed when stirring pace was increased from 500 rpm to 2000 rpm. The FTIR spectroscopy showed the absorption bands of the stretching modes of Zn-O between 500 cm⁻¹ to 525 cm⁻¹. The Thermal analysis studies revealed better stability for ZnO-NPs prepared at 2000 rpm (ZnO-2000 rpm). TGA revealed the weight loss between two main temperatures ranges viz. around (90 °C–120 °C) and (240 °C–280 °C). Finally, the effect of ZnO-NPs prepared at different stirring conditions on the growth of Gram-positive (Bacillus subtilis), Gram-negative (Escherichia coli) bacteria and a fungi (Candida albicans) were examined; which showed good antibacterial as well as antifungal properties. These findings introduce a simple, inexpensive process to synthesize ZnO-NPs using conventional methods without the use of sophisticated equipments and its application as a potent nano-antibiotic.

Green synthesis and characterization of silver nanoparticles using Ferula latisecta leaf extract and their application as a catalyst for the safe and simple one-pot preparation of spirooxindoles in water

In this research, Ag nanoparticles were prepared via plant extract and applied as an efficient catalyst in a three component reaction for the synthesis of spirooxindols.

Enhanced cell-wall damage mediated, antibacterial activity of core-shell ZnO@Ag heterojunction nanorods against Staphylococcus aureus and Pseudomonas aeruginosa

Hybrid ZnO@Ag core-shell nanorods have been synthesized by a synthetic strategy based on seed mediated growth. Formation of core-shell nanostructures was confirmed by UV- diffused reflectance spectroscopy (UV-DRS), X-ray diffraction studies, field emission scanning electron microscopy and high resolution transmission electron microscopy. UV-DRS analysis of hybrid core-shell nanorods suggests the possibility of interfacial electron transfer between surface anchored Ag nanoclusters and ZnO nanorods. Successful decoration of Ag nanoclusters with an average diameter of ~7 ± 0.5 nm was observed forming the heterojunctions on the surface of the ZnO nanorods. An enhanced antibacterial property was observed for the ZnO@Ag core-shell nanorods against both Staphylococcus aureus and Pseudomonas aeruginosa lbacteria. The synergetic antibacterial activity of ZnO@Ag nanorods was found to be more prominent against Gram-positive bacteria than Gram-negative bacteria. The plausible reason for this enhanced antibacterial activity of the core-shell nanorods can be attributed to the physical damage caused by the interaction of the material with outer cell wall layer due to the production of reactive oxygen species by interfacial electron transfer between ZnO nanorods and plasmonic Ag nanoclusters. Overall, the ZnO@Ag core-shell nanorods were found to be promising materials that could be developed further as an effective antibacterial agent against wide range of microorganisms to control spreading and persistence of bacterial infections.