Synthesis, Properties and Bioimaging Applications of Silver-Based Quantum Dots

Ag-based quantum dots (QDs) are semiconductor nanomaterials with exclusive electrooptical properties ideally adaptable for various biotechnological, chemical, and medical applications. Silver-based semiconductor nanocrystals have developed rapidly over the past decades. They have become a promising luminescent functional material for in vivo and in vitro fluorescent studies due to their ability to emit at the near-infrared (NIR) wavelength. In this review, we discuss the basic features of Ag-based QDs, the current status of classic (chemical) and novel methods (“green” synthesis) used to produce these QDs. Additionally, the advantages of using such organisms as bacteria, actinomycetes, fungi, algae, and plants for silver-based QDs biosynthesis have been discussed. The application of silver-based QDs as fluorophores for bioimaging application due to their fluorescence intensity, high quantum yield, fluorescent stability, and resistance to photobleaching has also been reviewed.

Photocatalytic activity of silica and silica-silver nanocolloids based on photo-induced formation of reactive oxygen species

Semiconductor nanomaterials are often proposed as photocatalysts for wastewater treatment; silica nanomaterials are still largely unexploited because their photocatalytic performances need improvements, especially under visible light. The present study is a proof-of-concept that amorphous silica colloids once submitted to the proper surface modifications change into an efficient photocatalyst even under low-energy illumination source. For this reason, silica-based colloidal nanomaterials, such as bare (SiO2 NPs), aminated (NH2-SiO2 NPs), and Ag NPs-decorated (Ag-SiO2 NPs) silica, are tested as photocatalysts for the degradation of 9-anthracenecarboxylic acid (9ACA), taken as a model aromatic compound. Interestingly, upon irradiation at 313 nm, NH2-SiO2 NPs induce 9ACA degradation, and the effect is even improved when Ag-SiO2 NPs are used. On the other hand, irradiation at 405 nm activates the plasmon of Ag-SiO2 NPs photocatalyst, providing a faster and more efficient photodegradation. The photodegradation experiments are also performed under white light illumination, employing a low-intensity fluorescent lamp, confirming satisfying efficiencies. The catalytic effect of SiO2-based nanoparticles is thought to originate from photo-excitable surface defects and Ag NP plasmons since the catalytic degradation takes place only when the 9ACA is adsorbed on the surface. In addition, the involvement of reactive oxygen species was demonstrated through a scavenger use, obtaining a yield of 17%. In conclusion, this work shows the applicability of silica-based nanoparticles as photocatalysts through the involvement of silica surface defects, confirming that the silica colloids can act as photocatalysts under irradiation with monochromatic and white light. Graphic abstract Silica and Ag-decorated silica colloids photosensitize the formation of Reactive Oxygen Species with 17% efficiencies. ROS are able to oxidase aromatic pollutants chemi-adsorbed on the surface of the colloids. Silica-silver nanocomposites present a photocatalytic activity useful to degrade aromatic compounds.

2D Semiconductor Nanomaterials and Heterostructures: Controlled Synthesis and Functional Applications

Two-dimensional (2D) semiconductors beyond graphene represent the thinnest stable known nanomaterials. Rapid growth of their family and applications during the last decade of the twenty-first century have brought unprecedented opportunities to the advanced nano- and opto-electronic technologies. In this article, we review the latest progress in findings on the developed 2D nanomaterials. Advanced synthesis techniques of these 2D nanomaterials and heterostructures were summarized and their novel applications were discussed. The fabrication techniques include the state-of-the-art developments of the vapor-phase-based deposition methods and novel van der Waals (vdW) exfoliation approaches for fabrication both amorphous and crystalline 2D nanomaterials with a particular focus on the chemical vapor deposition (CVD), atomic layer deposition (ALD) of 2D semiconductors and their heterostructures as well as on vdW exfoliation of 2D surface oxide films of liquid metals.

Effective Strategies, Mechanisms, and Photocatalytic Efficiency of Semiconductor Nanomaterials Incorporating rGO for Environmental Contaminant Degradation

The water pollution problems severely affect the natural water resources due to the large disposal of dyes, heavy metals, antibiotics, and pesticides. Advanced oxidation processes (AOP) have been developed using semiconductor nanomaterials as photocatalysts for water treatment as an essential strategy to minimize environmental pollution. Significant research efforts have been dedicated over the past few years to enhancing the photocatalytic efficiencies of semiconductor nanomaterials. Graphene-based composites created by integrating reduced graphene oxide (rGO) into various semiconductor nanomaterials enable the unique characteristics of graphene, such as the extended range of light absorption, the separation of charges, and the high capacity of adsorption of pollutants. Therefore, rGO-based composites improve the overall visible-light photocatalytic efficiency and lead to a new pathway for high-performance photocatalysts' potential applications. This brief review illustrates the strategies of combining rGO with various semiconductor nanomaterials and focuses primarily on modification and efficiency towards environmental contaminants.

Nitrogen Dioxide Sensing Technologies

The harmful impacts of nitrogen dioxide (NO2) include acid rain, respiratory diseases, allergy and photochemical smog. These also causes throat, eye and nose problems, cough, nausea and tiredness in extremely low concentrations (<10 ppm). So, detection and the sensing of NO2 gas is considered as one of the most important detecting techniques. Numerous electronic sensors, semiconductor nanomaterials, carbon nanotubes, graphene, activated carbon and mixed metal oxides have been investigated in order to detect and sense NO2. Several varieties of gas sensors including electrochemical, catalytic combustion, semiconductor and solid electrolyte gas sensors, have been industrialized.

Morphology Changes of Cu2O Nanoshells in the Photocatalysis

Background: It is meaningful to use semiconductor nanomaterials for degradation of organic compounds under irradiation of solar light. Introduction: Nano Cu2O is suitable for visible-light photocatalysis for the narrow band gap (~2.17 eV). However, few focus on the morphology changes of Cu2O in the process of photocatalysis. Methods: By two-step addition of reducer, porous Cu2O nanoshells (NSs) with almost 100% hollow structure were synthesized, characterized and used to photocatalyze MO in neutral solution at 30 C in air. Results: Cu2O NSs have high adsorption and good photocatalysis rates for MO. After photocatalysis, some new results were observed. Most chemical bonds of MO were broken, but part of sulfur containing group of MO left on the NSs. The morphology of Cu2O NSs was changed and lots of nanodebris was produced. Further experimental results showed some nanodebris was also observed after adsorption-desorption equilibrium (ADE). Without MO and only light irradiation of Cu2O suspension, little nanodebris appeared. The results of X-ray diffraction (XRD), scanning transmittance electron microscope (STEM) and high-resolution transmittance electron microscope (HRTEM) proved the composite of the nanodebris is Cu2O. The nanodebris are the nanosheets dropped off from the Cu2O NSs. Conclusion: For the porous Cu2O NSs are composed of Cu2O nanosheets with exposed 111 facets, which have strongest adsorption ability for MO and strongest catalysis performance. Light irradiation sped up this interaction and led to the Cu2O nanosheets dropping off from the Cu2O NSs. For the strong interaction between Cu+ and S, part of sulfur containing group of MO left on the NSs after photocatalysis.