Nano

Two-dimensional nanomaterials hold the most promising future, even surpassing conventional electromagnetic interference shields of heavy and corrosion-prone metallic materials. Among the materials discussed in this review, graphene and MXene prove to be the most promising materials owing to their flexibility, affordability and numerous attractive properties. Advancement in electromagnetic interference shielding materials has been a center of interest in research since the discovery of unwanted radiations emitted from the electromagnetic waves which cause severe damage to the environment, human beings and unshielded electronic devices. This review discusses some of the most recent preparation methodologies using the most effective nanomaterials, creating electromagnetic interference shielding materials at par in performance compared to conventional shielding methods.

Magnetic resonance imaging (MRI) is a noninvasive, imaging technique of soft tissues, providing the possibility for three-dimensional, high temporal and spatial resolution imaging. Gadolinium complexes are the most frequently used $T_1$-weighted contrast agents (CAs) to enhance the signal intensity of images. The toxicity of released Gd${}^{3+}$ has shifted the attention of researchers to manganese (Mn) oxide nanoparticles (NPs) as a $T_1$-weighted CA. Different phases and shapes of Mn oxide nanostructures with various coatings have been investigated to achieve the highest efficacy and lowest toxicity. In this review, engineering effects of Mn oxide nanostructures on image quality, toxicity and targeting have been studied. Switchable, multimodal imaging and theranostic systems, based on Mn oxide nanostructures, were also reviewed.

The adsorption mechanism of the branched quaternary ammonium salt Gemini surfactant (Gemini C₃) at the water-surfactant-quartz interfaces for both neutral and negatively charged quartz surfaces was studied by a molecular dynamics (MD) method. Initial and final configurations, distributions of the surfactant and its interaction with surfaces, the radial distribution function (RDF) of water molecules, and the mean square displacement (MSD) of the surfactant in bulk phase have been elucidated at the molecular level. The results showed that the adsorption of Gemini surfactants onto the hydrophilic quartz surface was driven by electrostatic interaction, which increased the hydrophobicity of the solid surface when the surfactant concentration was lower than critical micelle concentration (CMC). However, the contact angle only slightly increased since the surface tension decreased simultaneously with growing concentration. Monolayers were formed during the adsorption process of Gemini C₃ molecules on the quartz surface rather than a double layer when the concentration reached the CMC, indicating a gradual transformation of an extended monolayer adsorption configuration into a more compact one. The solid-liquid interfacial tension increased with the surfactant concentration and led to a significant increase of the contact angle. The simulation results were consistent with the experiments, which further revealed the microscopic adsorption mechanism of the Gemini C₃ surfactant onto the quartz surface, and provided theoretical guidance for controlling the wetting properties and surface modification of the rock.

Increasingly severe electromagnetic pollution problem boosts the demand for light weight microwave absorbing materials with high absorption capacity over wide frequency range. Biomass-derived porous carbon has been regarded as one of the promising candidates for microwave attenuation as the biomaterials are vastly available and renewable. Here, macadamia nutshell derived porous carbon (MPC) was fabricated by activated carbonization. Evidenced by the morphological results, the resulted MPC demonstrates three-dimensional frameworks with tubular skeletons. Owing to such hierarchical structures, the resulted composite MPC-filled paraffin composites exhibit a minimum reflection loss of $-$44.14dB and effective absorption bandwidth of 3.84GHz. Moreover, the resulted MPC can be explored as a practical absorber in a frequency range of 3.68–18.00GHz via tuning of the thickness. The analysis of microwave attenuation mechanism indicates that such outstanding microwave absorption capacity is attributed to hierarchical structure tuned impedance matching conditions and multiple attenuation mechanisms. All results in this work open the avenue for the development of nutshell derived sustainable microwave absorber with high absorption capacity as well as broad effective absorption bandwidth, boosting the utilizing of biomass resources.

The design and construction of semiconductor–metal heterojunctions are being considered to be an effective way to overcome the limited visible-light absorption of semiconductors. Herein, a facile and scale approach is reported for the first time to synthesize Cu/ZnO heterojunctions by one-step galvanic replacement between Zn and cuprous solution reaction. Two kinds of morphologies Cu/ZnO heterojunctions could be obtained by changing cuprous salt anion such as Br⁻, Cl⁻ and I⁻. A flower-like Cu/ZnO heterostructured is chosen as a representative to demonstrate the facility and enhanced photocatalytic performance toward Rhodamine B degradation under visible-light irradiation. Results showed flower-like Cu/ZnO heterojunctions have higher photocatalytic performance than the other two morphologies. The galvanic replacement growth mechanism of Cu/ZnO heterojunctions was also further investigated. It is found that Cu/ZnO heterojunctions formed from Zn and Cu₂O at an acid solution and room condition. This work indicates that galvanic replacement reaction at room temperature is an excellent technique to grow Cu/ZnO heterojunctions and demonstrates that the hole and electron transfer between Cu and ZnO can efficiently enhance their photocatalytic performance. This general method can also be further explored to guide the design of metal/metal oxide heterostructured on other substrates, such as Zn, Ni and Cu foils.

A selective and sensitive method was proposed for the determination of hydrazine by electrochemical deposition of Au nanodendrites (AuNDs) on the electropolymerized-2-(3,4-dihydroxybenzaldehyde) malononitrile (AuNDs/HBM/GCE). Deposition of AuNDs on the surface of HBM modified electrode effectively increased the electron transfer and active surface area. The surface analysis techniques substantiated the deposition of AuNDs and HBM molecules at the electrode surface. As-prepared modified electrode produced a sharp peak for hydrazine oxidation at $+0.08$ versus Ag/AgCl, with a significant negative potential shift (about 0.43V) compared with unmodified glassy carbon electrode (GCE). The proposed electrode showed a linear response over 0.2$\mu$M–2.4mM with the detection limit of 0.08$\mu$M ($Y_{\mathrm{\text{LOD}}}=Y_B+3\sigma )$. Moreover, AuNDs/HBM/GCE exhibited appropriate stability, selectivity and reproducibility. One of the brilliant advantages of the proposed method is the determination of hydrazine in the presence of hydroxylamine. The peaks of these two compounds are completely separate at $+0.08$ and $+0.20$V. Therefore, the fabricated electrode is capable of hydrazine quantification in real samples without apparent hydroxylamine interference.

The biodegradability of inorganic nanocarriers is one of the most critical issues in their further clinical translations. In this work, a manganese-doped approach was developed to endow inorganic mesoporous silica (SiO₂) nanospheres with pH-sensitive biodegradation. Manganese-doped mesoporous silica nanospheres (MMS) were prepared by in-situ doping method, with a particle diameter of 160–175 nm and pore diameter of 3–5nm by characterization of N₂ adsorption method, powder X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectrum, field emission scanning electron microscope and transmission electron microscope techniques. Quercetin was used as the model drug to load, and MMS loaded with quercetin (MMS–QUE) was surface-modified using a carboxymethyl chitosan (MMS–QUE–CMCS) to prevent quercetin leakage. Based on the dissolution characteristics of manganese ions and the swelling behavior of carboxymethyl chitosan, the MMS–QUE–CMCS could be degraded in response to acid. The MMS–QUE–CMCS delivery system exhibited a good pH-responsive release. The cytotoxicity test showed that the MMS–QUE–CMCS had a significant biocompatibility and an enhanced cytotoxicity, thus revealing that the MMS–QUE–CMCS was a promising delivery system.

A copper oxide (CuO) nanoparticle, a transition metal oxide with a wide variety of easy production methods, can be used as an antimicrobial agent against various types of bacteria. CuO nanoparticles were produced by the sol–gel method, annealed and structural characteristics and antimicrobial properties of these particles were investigated. Single-phase monoclinic of CuO nanoparticle formation was confirmed by X-ray powder diffraction (XRD) spectra, FTIR techniques, differential scanning calorimetry with thermal gravimetry were used to characterize. It was determined that annealing in the temperature range of 150–900^∘C affects both structure and particle size and antimicrobial characteristics. CuO nanoparticle size was found to be between about 25–70nm at 150–900^∘C annealing temperature, which does not have this wide temperature range in the literature. These results were supported by the TEM micrographs of the CuO nanoparticles observed at 150^∘C and 900^∘C. The antimicrobial activity of the synthesized nanoparticles was tested with the disc diffusion assay against Staphylococcus aureus, Escherichia coli, Agrobacterium tumefaciens, and yeast Pichia pastoris. The antimicrobial properties of the nanoparticles first increased and then decreased and disappeared as the annealing temperature increased. The antimicrobial properties of CuO nanoparticles disappeared at 750^∘C and above, while the maximum antimicrobial effect was at 300^∘C. The inhibition zones were examined and similar results were observed in all tested microorganisms.

In this paper, a simple method has been used to synthesize silver-molybdenum disulfide nanoparticles (Ag-MoS₂ NPs) with photothermal and physical inhibition of bacteria. The MoS₂ nanocarriers were obtained by an environment-friendly liquid-phase separation method. The coated Ag NPs with high antibacterial activity and fluorescence property endowed the synthesized Ag-MoS₂ NPs with the ability to be traced. The Ag-MoS₂ NPs had photothermal properties with a maximum photothermal increase of $72^{\circ }$C. The results of the dual photothermal–chemical antibacterial activity using Ag-MoS₂ NP carriers showed that Ag-MoS₂ NPs had broad-spectrum inhibition activity with MIC values up to $5.2\pm 0.3$$\mu$g/mL against Escherichia coli. The Ag-MoS₂ NPs were also used to destroy cell integrity by disrupting cell membranes and cell walls to achieve the inhibition of cell survival. The toxicity test in mice demonstrated the nontoxicity of Ag-MoS₂ NPs. Ag-MoS₂ NPs were studied for dual photothermal–chemical antibacterial activity, and the material reduced the amount of Ag NPs used, resulting in lower biotoxicity, hence providing a possible avenue for the clinical application of Ag NPs.

AgBr/zeolite photocatalysts with different mass ratios were synthesized by depositing AgBr on the surface of 4A zeolite via the one-step precipitation method. AgBr/zeolite with mass ratios of 1:1 exhibited the highest photocatalytic activity, resulting in the complete degradation of the methyl orange (MO) dye under visible-light irradiation for 30min. The photocatalysts were characterized by N₂ adsorption–desorption, scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–Vis diffused reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The AgBr particles around 4A zeolite were smaller than pure AgBr. The specific surface area of 1:1 AgBr/zeolite was much larger than that of pure AgBr, which indicates that 1:1 AgBr/zeolite possessed more active sites. The photocatalytic stability of 1:1 AgBr/zeolite was investigated, and MO degradation rate of 90.4% was achieved after five cycling runs. The trapping experiments showed that hydroxyl radical ($\cdot$OH), superoxide radical ($\cdot {\text{O}}_2^{-}$), and hole (h⁺) were the reactive species responsible for removing MO, and h⁺ played a key role in MO removal. A possible reaction mechanism in AgBr/zeolite photocatalytic system for MO degradation was proposed.