Chitosan modulated engineer tin dioxide nanoparticles well dispersed by reduced graphene oxide for high and stable lithium-ion storage

Tin based materials are widely investigated as a potential anode material for lithium-ion batteries. Effectively dispersing SnO₂ nanocrystals in carbonaceous supporting skeleton using simplified methods is both promising and challenging. In this work, water soluble chitosan (CS) chains are employed to modulate the redox coprecipitation reaction between stannous chloride (SnCl₂) and few-layered graphene oxide (GO), where the excessive restacking of the corresponding reduced graphene oxide sheets (RGO) has been effectively inhibited and the grain size of the in-situ formed SnO₂ nanoparticles have been significantly controlled. In particular, the CS molecules are gradually detached from the RGO sheets with the GO deoxygenation process, leaving only a small quantity of CS remnants in the intermediate SnO₂@CS@RGO sample. The final SnO₂/CSC/RGO sample with significantly improved microstructure is synthesized after a simple thermal treatment, which delivers a high specific capacity of 842.9 mAh g^-1 at 1000 mA·g^-1 for 1000 cycles in half cells and a specific capacity of 410.5 mAh g^-1 at 200 mA·g^-1 for 100 cycles in full cells. The reasons for the good lithium-ion storage performances for the SnO₂/CSC/RGO composite have been studied.

Fluorescence Properties of ZnOQDs-GO-g-C3N4 Nanocomposites

In this paper, the fluorescence properties of ZnOQD-GO-g-C3N4 composite materials (ZCGQDs) were studied. Firstly, the addition of a silane coupling agent (APTES) in the synthesis process was explored, and it was found that the addition of 0.04 g·mL-1 APTES had the largest relative fluorescence intensity and the highest quenching efficiency. The selectivity of ZCGQDs for metal ions was also investigated, and it was found that ZCGQDs showed good selectivity for Cu2+. ZCGQDs were optimally mixed with Cu2+ for 15 min. ZCGQDs also had good anti-interference capability toward Cu2+. There was a linear relationship between the concentration of Cu2+ and the fluorescence intensity of ZCGQDs in the range of 1~100 µM. The regression equation was found to be F0/F = 0.9687 + 0.12343C. The detection limit of Cu2+ was about 1.74 μM. The quenching mechanism was also analyzed.

L-cysteine embedded core-shell ZnO microspheres composed of nanoclusters enhances anticancer activity against liver and breast cancer cells

Nano-based products have become an apparent and effective option to treat liver cancer, which is a deadly disease, and minimize or eradicate these problems. The Core-shell ZnO microspheres composed of nanoclusters (ZnOMS-NCs) have shown that it is very worthwhile to administer the proliferation rate in HepG2 and MCF-7 cancer cells even at a very low concentration (5 μg/mL). ZnOMS-NCs were prepared through hydrothermal solution process and well characterized. The MTT assay revealed that the cytotoxic effects were dose-dependent (2.5 μg/mL-100 μg/mL) on ZnOMS-NCs. The diminished activity in cell viability induces the cytotoxicity response to the ZnOMS-NCs treatment of human cultured cells. The qPCR data showed that the cells (HepG2 and MCF-7) were exposed to ZnOMS-NCs and exhibited up-and downregulated mRNA expression of apoptotic and anti-apoptotic genes, respectively. In conclusion, flow cytometric data exhibited significant apoptosis induction in both cancer cell lines at low concentrations. The possible mechanism also describes the role of ZnOMS-NCs against cancer cells and their responses.

Zn-doped Tin monoxide nanobelt induced engineering a graphene and CNT supported Zn-doped Tin dioxide composite for Lithium-ion storage

In this work, a rapid coprecipitation reaction is developed to obtain nano-sized Zn-doped tin oxide samples (Zn-SnO-II or Zn-SnO₂-IV) for the first time by simply mixing tin ion (Sn²⁺ or Sn⁴⁺) and zinc ion (Zn²⁺) containing salts in a mild aqueous condition. Characterization results illustrate the Zn-SnO-II sample is constituted by an overwhelming quantity of Zn-doped SnO nanobelts and a small quantity of Zn-doped SnO₂ nanoparticles. The redox reaction between the Sn²⁺ ions from the Zn-SnO-II sample and the surface oxygen-containing functional groups from functionalized carbon nanotube (F-CNT) and graphene oxide (GO) leads to the formation of the final Zn-SnO₂/CNT@RGO composites. As an anode active material for lithium-ion batteries, the Zn-SnO₂/CNT@RGO product showed superior electrochemical performance than the controlled Zn-SnO₂/CNT and Zn-SnO₂/RGO samples, which had a high gravimetric capacity of 901.3 mAh·g^-1 at a high charge and discharge current of 1000 mA·g^-1 after 300 cycles and excellent rate capability. The reaction mechanism for the successful synthesis of the Zn-doped tin oxide samples has been proposed, and the insight into the outstanding lithium-ion storage performance for the Zn-SnO₂/CNT@RGO composite has been revealed. The synthetic processes for both the Zn-doped tin oxides and derived carbon supported composites are straightforward and involve no harsh conditions nor complicated treatment, which have good potential for massive production and application in wider fields.

Sodium carboxymethylcellulose induced engineering a porous carbon and graphene immobilized magnetite composite for lithium-ion storage

Immobilizing nanosized electrochemically active materials with supportive carbonaceous framework usually brings in improved lithium-ion storage performance. In this work, magnetite nanoparticles (Fe₃O₄) are stabilized by both porous carbon domains (PC) and reduced graphene oxide sheets (RGO) to form a hierarchical composite (Fe₃O₄@PC/RGO) via a straightforward approach. The PC confined iron nanoparticle intermediate sample (Fe@PC) was first fabricated, where sodium carboxymethylcellulose (Na-CMC) was employed not only as a cross-linker to trap ferric ions for synthesizing a Fe-CMC precursor sample, but also as the carbon source for PC domains and iron source for Fe nanoparticles in a pyrolysis process. The final redox reaction between Fe@PC and few-layered graphene oxide (GO) sheets contributed to the formation of Fe₃O₄ nanoparticles with reduced size, avoiding any severe aggregation or excessive exposure. The Fe₃O₄@PC/RGO sample delivered a specific capacity of 522.2 mAh·g^-1 under a current rate of 1000 mA·g^-1 for 650 cycles. The engineered Fe@PC and Fe₃O₄@PC/RGO samples have good prospects for application in wider fields.

Spray drying induced engineering a hierarchical reduced graphene oxide supported heterogeneous Tin dioxide and Zinc oxide for Lithium-ion storage

In this work, a hierarchical reduced graphene oxide (RGO) supportive matrix consisting of both larger two-dimensional RGO sheets and smaller three-dimensional RGO spheres was engineered with ZnO and SnO₂ nanoparticles immobilized. The ZnO and SnO₂ nanocrystals with controlled size were in sequence engineered on the surface of the RGO sheets during the deoxygenation of graphene oxide sample (GO), where the zinc-containing ZIF-8 sample and metal tin foil were used as precursors for ZnO and SnO₂, respectively. After a spray drying treatment and calcination, the final ZnO@SnO₂/RGO-H sample was obtained, which delivered an outstanding specific capacity of 982 mAh·g^-1 under a high current density of 1000 mA·g^-1 after 450 cycles. Benefitting from the unique hierarchical structure, the mechanical strength, ionic and electric conductivities of the ZnO@SnO₂/RGO-H sample have been simultaneously promoted. The joint contributions from pseudocapacitive and battery behaviors in lithium-ion storage processes bring in both large specific capacity and good rate capability. The industrially mature spray drying method for synthesizing RGO based hierarchical products can be further developed for wider applications.

Engineering tin dioxide quantum dots in a hierarchical graphite and graphene oxide framework for lithium-ion storage

The spontaneous aggregation and poor electronic conductivity are widely recognized as the main challenges for practically applied nano-sized tin dioxide-based anode candidates in lithium-ion batteries. This work describes a hierarchical graphite and graphene oxide (GO) framework stabilized tin dioxide quantum dot composite (SnO₂@C/GO), which is synthesized by a solid-state ball-milling treatment and a water-phase self-assembly process. Characterization results demonstrate the engineered inside nanostructured graphite and outside GO layers from the SnO₂@C/GO composite jointly contribute to a good immobilization effect for the SnO₂ quantum dots. The hierarchical carbonaceous matrix supported SnO₂ quantum dots could maintain good structure stability over a long cycling life under high current densities. As an anodic electrochemically active material for lithium-ion batteries, the SnO₂@C/GO composite shows a high reversible capacity of 1156 mAh·g^-1 at the current density of 1000 mA·g^-1 for 350 continual cycles as well as good rate performance. The large pseudocapacitive behavior in this electrode is favorable for promoting the lithium-ion storage capability under higher current densities. The whole synthetic route is simple and effective, which probably has good potential for further development to massively fabricate high-performance electrode active materials for energy storage.

Facile synthesis of a rod-like porous carbon framework confined magnetite nanoparticle composite for superior lithium-ion storage

This work demonstrates a streamlined method to engineer a rod-like porous carbon framework (RPC) confined magnetite nanoparticles composite (Fe₃O₄/RPC) starting from metallic iron and gallic acid (GA) solution. First, a mild redox reaction was triggered between Fe and GA to prepare a rod-shaped metal-organic framework (MOF) ferric gallate sample (Fe-GA). Then, the Fe-GA sample was calcinated to obtain a prototypic RPC supported metal iron nanoparticle intermediate sample (Fe/RPC). Finally, the Fe₃O₄/RPC composite was synthesized after a simple hydrothermal reaction. The Fe₃O₄/RPC composite exhibited competitive electrochemical behaviors, which has a high gravimetric capacity of 1140 mAh·g^-1 at a high charge and discharge current of 1000 mA·g^-1 after 300 cycles. The engineered RPC supportive matrix not only offers adequate voids to buffer the volume expansion from inside well-dispersed Fe₃O₄ nanoparticles, but also facilitates both the ionic and electronic transport during the electrochemical reactions. The overall material synthesis involves of no hazardous or expensive chemicals, which can be regarded to be a scalable and green approach. The obtained samples have a good potential to be further developed for wider applications.

Biocide mechanism of highly efficient and stable antimicrobial surfaces based on zinc oxide-reduced graphene oxide photocatalytic coatings

Highly efficient photoactive antimicrobial coatings were obtained using zinc oxide-reduced graphene oxide nanocomposites (ZnO-rGO). Their remarkable antibacterial activity and high stability demonstrated their potential use for photoactive biocide surfaces. The ZnO-rGO nanocomposites were prepared by the sol-gel technique to create photocatalytic surfaces by spin-coating. The coatings were deeply characterised and several tests were performed to assess the antibacterial mechanisms. rGO was homogeneously distributed as thin sheets decorated with ZnO nanoparticles. The surface roughness and the hydrophobicity increased with the incorporation of graphene. The ZnO-rGO coatings exhibited high activity against the Gram-positive bacterium Staphylococcus aureus. The 1 wt% rGO coated surfaces showed the highest antibacterial effect in only a few minutes of illumination with up to 5-log reduction in colony forming units, which remained essentially free of bacterial colonization and biofilm formation. We demonstrated that these coatings impaired the bacterial cells due to cell membrane damage and intracellular oxidative stress produced by the photogenerated reactive-oxygen species (ROS). The enhancement of the ZnO photocatalytic performance upon rGO incorporation is due to the increased detected generation of hydroxyl radicals, attributed to the reduction of electron-hole pair recombination. This intimate contact between both components also conveyed stability against zinc leaching and improved the coating adhesion.

Recent Developments in Carbon Quantum Dots: Properties, Fabrication Techniques, and Bio-Applications

Carbon dots have gained tremendous interest attributable to their unique features. Two approaches are involved in the fabrication of quantum dots (Top-down and Bottom-up). Most of the synthesis methods are usually multistep, required harsh conditions, and costly carbon sources that may have a toxic effect, therefore green synthesis is more preferable. Herein, the current review presents the green synthesis of carbon quantum dots (CQDs) and graphene quantum dots (GQDs) that having a wide range of potential applications in bio-sensing, cellular imaging, and drug delivery. However, some drawbacks and limitations are still unclear. Other biomedical and biotechnological applications are also highlighted.

Hierarchical goethite nanoparticle and tin dioxide quantum dot anchored on reduced graphene oxide for long life and high rate lithium-ion storage

The synergetic effect between two or more electrochemically active materials usually leads to superior lithium-ion storage performance. This work demonstrates a straightforward and effective approach to synthesize a reduced graphene oxide (RGO) encapsulated larger goethite (FeOOH) nanoparticles and smaller tin dioxide (SnO₂) quantum dots hierarchical composite (SnO₂@FeOOH/RGO). The synthesized SnO₂@FeOOH/RGO composite exhibits encouraging lithium-ion storage capability than controlled SnO₂/RGO and FeOOH/RGO samples with a stable specific capacity of 638 mAh·g^-1 under a high current rate of 1000 mA·g^-1 for 2000 continual cycles and good rate performance. The redox reaction between reductive metal-atoms or metal-ions and graphene oxide (GO) sheets guarantees an effective immobilization of corresponding nano-sized metal oxide and hydroxide crystals by the RGO framework. Furthermore, the engineered larger FeOOH crystals engage in lithium-ion storage and perform an ideal spacer between the restacked RGO sheets. Therefore, smaller SnO₂ quantum dots' inherent excellent rate capability is extensively promoted due to the improvement of electrolyte diffusion and electron transfer condition. The sample design and fabrication method in this work might be developed for broader applications.

Journey of ZnO quantum dots from undoped to rare-earth and transition metal-doped and their applications

Currently, developments in the field of quantum dots (QDs) have attracted researchers worldwide. A large variety of QDs have been discovered in the few years, which have excellent optoelectronic, antibacterial, magnetic, and other properties. However, ZnO is the single known material that can exist in the quantum state and can hold all the above properties. There is a lot of work going on in this field and we will be shorthanded if we do not accommodate this treasure at one place. This manuscript will prove to be a milestone in this noble cause. Having a tremendous potential, there is a developing enthusiasm toward the application of ZnO QDs in diverse areas. Sol-gel method being the simplest is the widely-favored synthetic method. Synthesis via this method is largely affected by a number of factors such as the reaction temperature, duration of the reaction, type of solvent, pH of the solution, and the precipitating agent. Doping enhances the optical, magnetic, anti-bacterial, anti-microbial, and other properties of ZnO QDs. However, doping elements reside mostly on the surface of the QDs. The presence of doping elements inside the core is still a major challenge for doping techniques. In this review article, we have focused on pure, rare-earth, and transition metal-doped ZnO QD properties, and the various synthetic processes and applications. Quantum confinement effect is present in nearly every aspect of the QDs. The effect of quantum confinement has also been summarized in this manuscript. Furthermore, the doping of rare earth elements and transition metal, synthetic methods for different organic molecule-capped ZnO QDs, mechanisms for reactive oxygen species (ROS) generation, drug delivery system for cancer treatment, and many more application are discussed in this paper.

Engineering zinc ferrite nanoparticles in a hierarchical graphene and carbon nanotube framework for improved lithium-ion storage

This work presents the successful fabrication of a composite made of multi-walled carbon nanotubes and reduced graphene oxide, with immobilized zinc ferrite nanoparticles (ZnFe₂O₄@CNT/RGO). Functionalized CNT (F-CNT) and few-layered graphene oxide (GO) not only works as a precursor for the hierarchical CNT/RGO skeleton, but also participates in the redox reactions with zinc and ferrous ions to synthesize the intermediate products ZnO@CNT and FeOOH@RGO, respectively. A ZnO@CNT/FeOOH@RGO composite is obtained by through the spontaneous assembly process between the above intermediate species, and the final ZnFe₂O₄@CNT/RGO composite is fabricated through a simple solid-state reaction. The ZnFe₂O₄@CNT/RGO composite delivers a reversible capacity of about 1250 mAh·g^-1 after 100 cycles at a low current of 200 mA·g^-1, about 1100 mAh·g^-1 after 300 cycles at a high current of 1000 mA·g^-1. It has been verified that an increase in battery performance can be attributed to the engineered hierarchical CNT/RGO supportive skeleton, the generation of smaller electrochemically active ZnO and Fe₂O₃ crystals, and pseudocapacitive behavior. The sample design and preparation method in this work are both economical and scalable, allowing further development and use in other applications.

Simple and effective synthesis of zinc ferrite nanoparticle immobilized by reduced graphene oxide as anode for lithium-ion batteries

In this work, a simple and effective method is developed to synthesize zinc ferrite nanoparticles (ZnFe₂O₄) in a redox coprecipitation reaction system containing only ferrous and zinc salt followed by a solid-state reaction. On this foundation, ZnFe₂O₄ nanoparticles with reduced size are further immobilized by reduced graphene oxide (RGO) to engineer a ZnFe₂O₄/RGO composite by simply introducing graphene oxide (GO) in the above reaction system. The ZnFe₂O₄/RGO composite electrode exhibits attractive lithium-ion storage capability with a reversible capacity of about 760 mAh·g^-1 for 200 charge/discharge cycles and 603 mAh·g^-1 for 700 cycles under a current rate of 1.0 A·g^-1. The robust and porous RGO supporting framework, well immobilized ZnFe₂O₄ nanoparticles with controlled size and pseudocapacitive behavior of the composite jointly ensure the good battery performance. Moreover, the synthetic route for ZnFe₂O₄ nanoparticles and ZnFe₂O₄/RGO composite is simple and economic, which may be further developed for massive production and applied in other fields.

Laser-assisted synthesis of gold-graphene oxide nanocomposites: effect of pulse duration

Laser photoreduction of metal ions onto graphene oxide (GO) is a facile, environmentally friendly method to produce functional metal-GO nanocomposites for a variety of applications. This work compares Au-GO nanocomposites prepared by photoreduction of [AuCl₄]^- in aqueous GO solution using laser pulses of nanosecond (ns) and femtosecond (fs) duration. The presence of GO significantly accelerates the [AuCl₄]^- photoreduction rate, with a more pronounced effect using ns laser pulses. This difference is rationalized in terms of the stronger interaction of the 532 nm laser wavelength and long pulse duration with the GO. Both the ns and fs lasers produce significant yields of sub-4 nm Au nanoparticles attached to GO, albeit with different size distributions: a broad 5.8 ± 1.9 nm distribution for the ns laser and two distinct distributions of 3.5 ± 0.8 and 10.1 ± 1.4 nm for the fs laser. Despite these differences, both Au-GO nanocomposites had the same high catalytic activity towards p-nitrophenol reduction as compared to unsupported 4-5 nm Au nanoparticles. These results point to the key role of GO photoexcitation in catalyzing metal ion reduction and indicate that both ns and fs lasers are suitable for producing functional metal-GO nanocomposites.

Template-free synthesis and lithium-ion storage performance of multiple ZnO nanoparticles encapsulated in hollow amorphous carbon shells

Due to the limited utilization of electrode materials, the rational design and facile synthesis of composite structures are still challenging issues for lithium-ion batteries (LIBs). Herein, a simple approach has been developed to prepare multiple core–shell structures of ZnO nanoparticles (NPs) encapsulated in hollow amorphous carbon (AC) shells. The as-synthesized ZnO@AC composites showed a uniform dispersion of ZnO NPs, compliant buffer AC shells, and nanoscale void spaces between the ZnO NP cores and AC shells. As a result of their structural merits, the ZnO@AC composites were evaluated as anode materials for LIBs and delivered enhanced coulombic efficiency, high reversible capacity, high rate capability, and improved cycling stability.

Core–shell structure of ZnO@amorphous carbon shell was synthesized using a simple and effective method, and exhibited excellent electrochemical performance as anode of lithium-ion batteries.

Controlled engineering of nano-sized FeOOH@ZnO hetero-structures on reduced graphene oxide for lithium-ion storage and photo-Fenton reaction

In this work, a nano-sized goethite and zinc oxide hetero-structure (FeOOH@ZnO) dispersed on reduced graphene oxide (RGO) sheets was synthesized for the first time to construct a ternary composite (FeOOH@ZnO/RGO) via a stepped graphene oxide (GO) deoxygenation process.