Localized surface plasmon resonance enhanced photocatalysis: an experimental and theoretical mechanistic investigation

Titanium dioxide (TiO₂) is an advantageous material in catalytic photodegradation due to its low cost, high stability, and considerably higher efficiency when compared to other semiconductors. However, the need for artificial radiation sources in the UV range is a limitation to its use in wastewater remediation. In this context, Localized Surface Plasmon Resonance (LSPR) has been shown to enhance the photoexcitation of charge carriers in the semiconductor. In the present work, the investigation of catalytic photodegradation of phenol solution under distinct excitation by UV-visible or just visible radiation, employing three TiO₂ based plasmonic catalysts, was conducted. Spherical silver nanoparticles which present LSPR along the TiO₂ bandgap energy and electrically insulated silver nanoparticles were employed. Gold nanoparticles, which present low energy LSPR, were also employed in order to compare the excitation efficiency. Discrete dipole approximation simulations were carried out in order to verify the electric field enhancement and penetration at the semiconductor surface of each plasmonic catalyst. The results presented here may help to shed some light with respect to the contribution of plasmonic photocatalysts and the charge transfer mechanism in catalysts containing plasmonic structures.

A theoretical (DDA simulation) and experimental (phenol degradation) study has shown the LSPR from Ag and Ag@SiO₂ NPs to contribute to better TiO₂ photocatalytic performances. Au NPs has shown very low contribution, due to its low energy LSPR.     

Gold nanoparticle decorated titania for sustainable environmental remediation: green synthesis,enhanced surface adsorption and synergistic photocatalysis

Developing materials for efficient environmental remediation via cheap, nontoxic and environmentally benign routes remains a challenge for the scientific community. Here, a novel, facile, and green synthetic approach to prepare gold nanoparticle decorated TiO₂ (Au/TiO₂) nanocomposites for sustainable environmental remediation is reported. The synthesis involved only TiO₂, metal precursor and green tea, obviating the need for any solvents and/or harsh chemical reducing or stabilizing agents, and was efficiently conducted at 50 °C, indicating the prominent sustainability of the novel synthetic approach. The synthesis indicated notable atom economy, akin to that observed in a typical chemical mediated synthesis while high-resolution transmission electron microscopy (HRTEM) findings suggest the presence of a pertinent decoration of spherical and homogeneous gold nanoparticles on the titania surface. Notably, the Au/TiO₂ nanocomposite demonstrated appreciable stability during preparation, subsequent processing and prolonged storage. Further, the nanocomposite was found to have a superior adsorption capacity of 8185 mg g⁻¹ towards methylene blue (MB) in solution using the Freundlich isotherm model, while the rate constants for the photocatalytic degradation of MB on the nanocomposite under UV irradiation indicated a 4.2-fold improvement compared to that of bare TiO₂. Hence, this novel green synthesized Au/TiO₂ nanocomposite shows promising potential for sustainable environmental remediation via efficient contaminant capture and subsequent synergistic photocatalysis.

Green synthesis of gold nanoparticle decorated titania for enhanced surface adsorption and synergistic photocatalysis.     

Facile construction of a ZIF-67/AgCl/Ag heterojunction via chemical etching and surface ion exchange strategy for enhanced visible light driven photocatalysis

It is of great importance to design and fabricate heterojunction photocatalysts to improve photocatalytic performance. In this work, a novel ZIF-67/AgCl/Ag heterojunction photocatalyst was successfully synthesized by a facile chemical etching, deposition–precipitation, light-induced reduction approach. After chemical etching by a AgNO₃ precursor, the crystal size of ZIF-67 decreased remarkably together with the replacement of Co²⁺ in the framework of ZIF-67 by Ag⁺via surface ion exchange. As a result, optical and electrochemical measurements indicated that the separation efficiency of light-induced electrons and holes obviously increased due to the formation of a ZIF-67/AgCl/Ag heterojunction and the surface plasmon resonance of Ag⁰. Meanwhile, the corresponding kinetic rate constant of ZIF-67/AgCl/Ag was estimated to be 0.1615 min⁻¹, which was 17, 7.76 and 2.67 times as high as that of individual ZIF-67, AgCl and ZIF-67/AgCl, respectively. The ZIF-67/AgCl/Ag photocatalyst also exhibited good stability and reusability in the process of photodegradation. This work demonstrated a high efficiency photocatalyst for providing new sights into the preparation of a highly efficient MOF-based heterojunction photocatalyst and its potential applications in water purification.

It is of great importance to design and fabricate heterojunction photocatalysts to improve photocatalytic performance.     

Hierarchical Ag nanostructures on Sn-doped indium oxide nano-branches: super-hydrophobic surface for surface-enhanced Raman scattering

Herein, we fabricated a super-hydrophobic SERS substrate using Sn-doped indium oxide (Indium-tin-oxide: ITO) nano-branches as a template. ITO nano-branches with tens of nanometer diameter are first fabricated through the vapor–liquid–solid (VLS) growth to provide roughness of the substrate. 10 nm thickness of Ag thin film was deposited and then treated with the post-annealing process to create numerous air-pockets in the Ag film, forming a hierarchical Ag nanostructures. The resulting substrate obtained Cassie''s wetting property with a water contact angle of 151°. Compared to the normal hydrophobic Ag nanoparticle substrate, increase of about 4.25-fold higher SERS signal was obtained for 7 μL of rhodamine 6G aqueous solutions.

Herein, we fabricated a super-hydrophobic SERS substrate using Sn-doped indium oxide (Indium-tin-oxide: ITO) nano-branches as a template.     

Large-scale self-organized gold nanostructures with bidirectional plasmon resonances for SERS

Efficient substrates for surface-enhanced Raman spectroscopy (SERS) are under constant development, since time-consuming and costly fabrication routines are often an issue for high-throughput spectroscopy applications. In this research, we use a two-step fabrication method to produce self-organized parallel-oriented plasmonic gold nanostructures. The fabrication routine is ready for wafer-scale production involving only low-energy ion beam irradiation and metal deposition. The optical spectroscopy features of the resulting structures show a successful bidirectional plasmonic response. The localized surface plasmon resonances (LSPRs) of each direction are independent from each other and can be tuned by the fabrication parameters. This ability to tune the LSPR characteristics allows the development of optimized plasmonic nanostructures to match different laser excitations and optical transitions for any arbitrary analyte. Moreover, in this study, we probe the polarization and wavelength dependence of such bidirectional plasmonic nanostructures by a complementary spectroscopic ellipsometry and Raman spectroscopy analysis. We observe a significant signal amplification by the SERS substrates and determine enhancement factors of over a thousand times. We also perform finite element method-based calculations of the electromagnetic enhancement for the SERS signal provided by the plasmonic nanostructures. The calculations are based on realistic models constructed using the same particle sizes and shapes experimentally determined by scanning electron microscopy. The spatial distribution of electric field enhancement shows some dispersion in the LSPR, which is a direct consequence of the semi-random distribution of hotspots. The signal enhancement is highly efficient, making our SERS substrates attractive candidates for high-throughput chemical sensing applications in which directionality, chemical stability, and large-scale fabrication are essential requirements.

Here we present a two-step fabrication of large-scale self-organized gold nanostructures for multicolor surface-enhanced Raman spectroscopy (SERS). We studied the morphology and plasmonic responses of our substrates and performed optical simulations.     

Ultrasensitive biosensors based on waveguide-coupled long-range surface plasmon resonance (WC-LRSPR) for enhanced fluorescence spectroscopy

We investigated the coupling phenomenon between plasmonic resonance and waveguide modes through theoretical and experimental parametric analyses on the bimetallic waveguide-coupled long-range surface plasmon resonance (Bi-WCLRSPR) structure. The calculation results indicated that the multi-plasmonic coupling gives rise to the enhanced depth-to-width ratio of the reflection dip compared to that of LRSPR excited using a single set of Ag and Teflon. The optimized thickness of Ag(40 nm)/Teflon(700 nm)/Ag(5 nm)/Au(5 nm) was obtained and generated the highest plasmon intensity enhancement, which was 2.38 folds in comparison to the conventional bimetallic surface plasmon resonance (SPR) configuration (Ag/Au). 17β-Estradiol was used in the fluorescence enhancement experiment by the reflection geometry-based system, wherein the excitation light source was on the side of a WC-LRSPR chip opposite to that of the light detection unit. The phenomenon of surface plasmon-couple emission (SPCE) depends on the number of 17β-estradiol molecule promoters from female sex steroid hormones, which demonstrated a limit of detection (LOD) of 2 pg mL⁻¹ and 1.47-fold fluorescence improvement as compared to the non-coated material on the surface of pristine glass. This enhanced WC-LRSPR can readily find application in fluorescence escalation needed in cases where a weak fluorescence signal is predicted, such as the small volume of liquid containing fluorescent dyes in biological diagnosis.

We investigated the coupling phenomenon between plasmonic resonance and waveguide modes through theoretical and experimental parametric analyses on the bimetallic waveguide-coupled long-range surface plasmon resonance (Bi-WCLRSPR) structure.     

Modeling of the surface plasmon resonance tunability of silver/gold core–shell nanostructures

Tunable plasmonic noble metal nanoparticles are indispensable for chemical sensors and optical near field enhancement applications. Laser wavelengths within the absorption spectrum of the nanoparticle and Localized Surface Plasmon Resonances (LSPR) in the visible and near infrared range are the key points to be met for the successful utilization in the field of aforementioned high sensitivity sensors. This way, Surface Enhanced Raman Spectroscopy (SERS) has been pushed to the sensitivity level of single molecule. The tunability, i.e. the modulation of the surface plasmon resonance wavelength as a function of the ambient refractive index is one of the important criteria to be understood clearly. Among various noble metals, gold and silver nanoparticles have the strongest surface enhancement factors for the Raman signal and their tunability for many practical applications has been experimentally demonstrated. We present a comprehensive numerical investigation by means of a finite element analysis on Ag/Au core–shell nanospheres including agglomerated and non-agglomerated dimers. Tunability as a function of shell thickness, total nanosphere radius and fraction of overlap between the dimer is discussed. Our studies show that tunability is considerably affected by the nanosphere radius rather than the shell thickness. These findings may be helpful in the synthesis of nanoplasmonic structures, especially related to an optimized use of gold as the shell material for the targeted application.

Tunable plasmonic noble metal nanoparticles are indispensable for chemical sensors and optical near field enhancement applications.     

NiO decorated CeO2 nanostructures as room temperature isopropanol gas sensors

Heterostructures developed using CeO₂ show promising peculiarities in the field of metal oxide gas sensors due to the great variations in the resistance during the adsorption and desorption processes. NiO decorated CeO₂ nanostructures (NiO/CeO₂) were synthesized via a facile two-step process. High resolution transmission electron microscopy (HRTEM) results revealed the perfect decoration of NiO on the CeO₂ surface. The porous nature of the NiO/CeO₂ sensor surface was confirmed from scanning electron microscopy (SEM) analysis. Gas sensing studies of pristine CeO₂ and NiO/CeO₂ sensors were performed under room conditions and enhanced gas sensing properties for the NiO/CeO₂ sensor towards isopropanol were observed. Decoration of NiO on the CeO₂ surface develops a built-in potential at the interface of NiO and CeO₂ which played a vital role in the superior sensing performance of the NiO/CeO₂ sensor. Sharp response and recovery times (15 s/19 s) were observed for the NiO/CeO₂ sensor towards 100 ppm isopropanol at room temperature. Long-term stability of the NiO/CeO₂ sensor was also studied and discussed. From all the results it is concluded that the decoration of NiO on the CeO₂ surface could significantly enhance the sensing performance and it has great advantages in designing best performing isopropanol gas sensors.

NiO decorated CeO₂ nanostructures favor enhanced sensing performance towards isopropanol even at room temperature.     

Controllable synthesis of coloured Ag0/AgCl with spectral analysis for photocatalysis

Broad spectrum absorption of semiconductor photocatalysts is an essential requirement to achieve the best values of solar energy utilization. Here, through precise surface state adjustment, coaxial tri-cubic Ag⁰/AgCl materials with distinct apparent colours (blue and fuchsia) were successfully fabricated. The reasons for the different colour generation of the Ag⁰/AgCl materials were investigated by performing corresponding spectrum analysis. It was revealed that Ag⁰/AgCl-blue and Ag⁰/AgCl-fuchsia crystals could efficiently boost the photon energy harvesting, spanning from the UV to near-infrared spectral region (250–800 nm), and achieved 2.6 and 5.4 times the wastewater degradation efficiency of AgCl-white. Simultaneously, these two fresh coloured candidates were demonstrated to have preferable photocatalytic CO₂ photoreduction capability, with yields of ∼3.6 (Ag⁰/AgCl-fuchsia) and 2.6 (Ag⁰/AgCl-blue) times that of AgCl-white. It is expected that this work will provide a beneficial perspective for understanding the solar absorption feature at both the major structure modulation and particular surface state regulation level.

Through surface state modification, distinctly coloured AgCl (blue and fuchsia) materials have been successfully fabricated and exhibit a broader absorption region than normal white-coloured AgCl crystals for photocatalytic reactions.     

Plasmonic Ag decorated CdMoO4 as an efficient photocatalyst for solar hydrogen production

The synthesis of Ag-nanoparticle-decorated CdMoO₄ and its photocatalytic activity towards hydrogen generation under sunlight has been demonstrated. The CdMoO₄ samples were synthesized by a simple hydrothermal approach in which Ag nanoparticles were in situ decorated on the surface of CdMoO₄. A morphological study showed that 5 nm spherical Ag nanoparticles were homogeneously distributed on the surface of CdMoO₄ particles. The UV/DRS spectra show that the band gap of CdMoO₄ was narrowed by the incorporation of a small amount of Ag nanoparticles. The surface plasmonic effect of Ag shows broad absorption in the visible region. The enhanced photocatalytic hydrogen production activities of all the samples were evaluated by using methanol as a sacrificial reagent in water under natural sunlight conditions. The results suggest that the rate of photocatalytic hydrogen production using CdMoO₄ can be significantly improved by loading 2% Ag nanoparticles: i.e. 2465 μmol h⁻¹ g⁻¹ for a 15 mg catalyst. The strong excitation of surface plasmon resonance (SPR) absorption by the Ag nanoparticles was found in the Ag-loaded samples. In this system, the role of Ag nanoparticles on the surface of CdMoO₄ has been discussed. In particular, the SPR effect is responsible for higher hydrogen evolution under natural sunlight because of broad absorption in the visible region. The current study could provide new insights for designing metal/semiconductor interface systems to harvest solar light for solar fuel generation.

Plasmonic enhancement of photocatalytic hydrogen generation is demonstrated using hierarchical Ag decorated CdMoO₄ synthesized using a hydrothermal method.     

Facet-, composition- and wavelength-dependent photocatalysis of Ag2MoO4

Faceted β-Ag₂MoO₄ microcrystals are prepared by controlled nucleation and growth in diethylene glycol (DEG) or dimethylsulfoxide (DMSO). Both serve as solvents for the liquid-phase synthesis and surface-active agents for the formation of faceted microcrystals. Due to its reducing properties, truncated β-Ag₂MoO₄@Ag octahedra are obtained in DEG. The synthesis in DMSO allows avoiding the formation of elemental silver and results in β-Ag₂MoO₄ cubes and cuboctahedra. Due to its band gap of 3.2 eV, photocatalytic activation of β-Ag₂MoO₄ is only possible under UV-light. To enable β-Ag₂MoO₄ for absorption of visible light, silver-coated β-Ag₂MoO₄@Ag and Ag₂(Mo_0.95Cr_0.05)O₄ with partial substitution of [MoO₄]²⁻ by [CrO₄]²⁻ were prepared, too. The photocatalytic activity of all the faceted microcrystals (truncated octahedra, cubes, cuboctahedra) and compositions (β-Ag₂MoO₄, β-Ag₂MoO₄@Ag, β-Ag₂(Mo_0.95Cr_0.05)O₄) is compared with regard to the photocatalytic decomposition of rhodamine B and the influence of the respective faceting, composition and wavelength.

Faceted β-Ag₂MoO₄ microcrystals are prepared by controlled nucleation and growth in diethylene glycol (DEG) or dimethylsulfoxide (DMSO).     

On the photocatalysis evolution of heteroatom-doped Ag4M2 nanoclusters

Atomically precise metal nanoclusters doped with one or more heteroatom of other metals have exhibited extraordinary catalytic properties. Here we report a series of thiolate-protected Ag₄M₂ (M is dopant Ni, Pd and Pt) nanoclusters that adopt a similar structural framework like a distorted hexahedron, in which four Ag atoms are located at the midpoints of four side edges and two metal heteroatoms reside on the centres of the top and the bottom planes. The opposite orders of the catalytic performances of the three catalysts for the photocatalytic degradation of the methyl orange and rhodamine B dyes are found, which is attributed to two different types of inter-molecular recombination mechanisms. In both photocatalytic systems, both the catalyst and the dye are visible-light active, and the inter-molecular recombination of the photo-excited hole in the catalyst and the photo-excited electron in the dye leads to charge separation across the system comprising the catalyst and the dye. The study represents an important step towards developing the precise tailoring of the composition and structure to control the physicochemical properties of metal nanoclusters.

The structurally similar Ag₄Ni₂, Ag₄Pd₂ and Ag₄Pt₂ clusters exhibit a distinct activity evolution in photocatalytic reactions.     

Yolk–shell nanostructures: synthesis,photocatalysis and interfacial charge dynamics

Solar energy has long been regarded as a promising alternative and sustainable energy source. In this regard, photocatalysts emerge as a versatile paradigm that can practically transform solar energy into chemical energy. At present, unsatisfactory conversion efficiency is a major obstacle to the widespread deployment of photocatalysis technology. Many structural engineering strategies have been proposed to address the issue of insufficient activity for semiconductor photocatalysts. Among them, creation of yolk–shell nanostructures which possess many beneficial features, such as large surface area, efficient light harvesting, homogeneous catalytic environment and enhanced molecular diffusion kinetics, has attracted particular attention. This review summarizes the developments that have been made for the preparation and photocatalytic applications of yolk–shell nanostructures. Additional focus is placed on the realization of interfacial charge dynamics and the possibility of achieving spatial separation of charge carriers for this unique nanoarchitecture as charge transfer is the most critical factor determining the overall photocatalytic efficiency. A future perspective that can facilitate the advancement of using yolk–shell nanostructures in sophisticated photocatalytic systems is also presented.

This review gives a comprehensive retrospection on the preparation and photocatalytic applications of yolk–shell nanostructures with additional focus on the realization of interfacial charge dynamics.     

Localized surface plasmon resonance based biosensing

Introduction: Bioanalytical sensing based on the principle of localized surface plasmon resonance experiences is currently an extremely rapid development. Novel sensors with new kinds of plasmonic transducers and innovative concepts for the signal development as well as read-out principles were identified. This review will give an overview of the development of this field.

Areas covered: The focus is primarily on types of transducers by preparation or dimension, factors for optimal sensing concepts and the critical view of the usability of these devices as innovative sensors for bioanalytical applications.

Expert commentary: Plasmonic sensor devices offer a high potential for future biosensing given that limiting factors such as long-time stability of the transducers, the required high sensitivity and the cost-efficient production are addressed. For higher sensitivity, the design of the sensor in shape and material has to be combined with optimal enhancement strategies. Plasmonic nanoparticles from bottom-up synthesis with a post-synthetic processing show a high potential for cost-efficient sensor production. Regarding the measurement principle, LSPRi offers a large potential for multiplex sensors and can provide a high-throughput as well as highly paralleled sensing. The main trends are expected towards optimal LSPR concepts which represent cost-efficient and robust point-of-care solutions, and the use of multiplexed devices for clinical applications.     

Ag nanoparticle decorated MnO2 flakes as flexible SERS substrates for rhodamine 6G detection

Smart design of advanced substrates for surface-enhanced Raman scattering (SERS) activity is challenging but vital. Herein, we synthesized a new kind of AgNPs/MnO₂@Al flexible substrate as a SERS substrate for the detection of the analyte rhodamine 6G (R6G). The fabrication of porous MnO₂ nanoflakes on Al foil was conducted via a facile hydrothermal strategy. Owing to the large active surface area of the MnO₂ nanoflakes, the Ag nanoparticles were immobilized and displayed superior SERS performance with a low detection concentration of 1 × 10⁻⁶ M for R6G. In addition, the SERS performance was found to be strongly related to the morphology of the MnO₂@Al substrate material. Our smart design may provide a new method of construction for other advanced SERS substrates for the detection of R6G.

In this work, we synthesized a new kind of AgNPs/MnO₂@Al flexible substrate as a SERS substrate for the detection of analyte Rhodamine 6G (R6G), which displayed superior SERS performance with low detection concentration of 1 × 10^–6 M for R6G.     

DFT calculation and analysis of the gas sensing mechanism of methoxy propanol on Ag decorated SnO2 (110) surface

Methoxy propanol has been widely used in modern industry and consumer products. Inhalation or skin exposure to methoxy propanol for a long period would bring about safety challenges on human habitat and health. Ag decorated SnO₂ mesoporous material has been synthesized and shown to exhibit high sensitivity and good selectivity to methoxy propanol among other interferential VOC gases. Density Functional Theory study were conducted to yield insight into the surface–adsorbate interactions and therefore the gas sensing improvement mechanism by presenting accurate energetic and electronic properties for the Ag/SnO₂ system. Firstly, an electron transfer model on Ag and SnO₂ grain interface was put forward to illustrate the methoxy propanol gas sensing mechanism. Then, a three-layer adsorption model (TLAM) was proposed to investigate methoxy propanol gas sensing properties on a SnO₂ (110) surface. In the TLAM method, taking SnO₂ (110) surface for the basis, layer 1 illustrates the decoration of metal Ag on SnO₂ (110) surface. Layer 2 represents the adsorption of molecular oxygen on metal Ag decorated SnO₂ (110) surface. Layer 3 indicates the adsorption of methoxy propanol, and for comparison, three other VOC gases (namely, ethanol, isopropanol and p-xylene) on Ag decorated SnO₂ (110) surface with oxygen species pre-adsorbed consecutively. All the adsorption processes were calculated by means of Density Functional Theory method; the adsorption energy, net charge transfer, DOS, PDOS and also experimental data were utilized to investigate the methoxy propanol gas sensing mechanism on Ag decorated SnO₂ (110) surface with oxygen species pre-adsorbed.

Methoxy propanol has been widely used in modern industry and consumer products.     

Facile synthesis of multi-type carbon doped and modified nano-TiO2 for enhanced visible-light photocatalysis

Nano-TiO₂ is a type of environment-friendly and inexpensive substance that could be used for photocatalytic degradation processes. In this study, the multi-type carbon species doped and modified anatase nano-TiO₂ was innovatively synthesized and developed to overcome the deficiency of common nano-TiO₂ photocatalysts. The multi-type carbon species were derived from tetrabutyl titanate and ethanol as the internal and external carbon sources, respectively. Meanwhile, diverse characterization methods were applied to investigate the morphology and surface properties of the photocatalyst. Finally, the visible-light photocatalytic degradation activity of the collected samples was evaluated by using methyl orange as a model pollutant. The promotion mechanism of multi-type carbon species in the photocatalytic process was also discussed and reported. The results in this work show that the doping and modification of multi-type carbon species successfully narrows the bandgap of nano-TiO₂ to expand the light absorption range, reduces the valence band position to improve the oxidation ability of photogenerated holes, and promotes the separation of photogenerated charge carriers to improve quantum efficiency. In addition, the further modification of the external carbon source can promote the surface adsorption of MO and stabilize the multi-type carbon species on the surface of nano-TiO₂.

The synergistic modification of nano-TiO₂ by multi-type carbon species results in excellent and stable visible-light photocatalytic degradation activity.     

Cu nanoparticles decorated WS2 nanosheets as a lubricant additive for enhanced tribological performance

Tungsten disulfide–polydopamine–copper (WS₂–PDA–Cu) nanocomposites were first prepared by a green and effective biomimetic strategy and then used as a lubricant additive in polyalkylene glycol (PAG). The biomimetic strategy is inspired by the adhesive proteins in mussels. WS₂ nanosheets were decorated by uniformly dispersed Cu nanoparticles (Cu NPs). The WS₂–PDA–Cu nanocomposites with good dispersion stability, showed better friction reducing and anti-wear properties than WS₂, Cu NPs and WS₂–Cu dispersed in PAG base oil. The average friction coefficient and wear volume were reduced by 33.56% and 97.95%, respectively, at 150 °C under a load of 100 N for the optimal concentration of 0.9 wt%. The lubrication mechanism was discussed.

Tungsten disulfide–polydopamine–copper (WS₂–PDA–Cu) nanocomposites were first prepared by a green and effective biomimetic strategy and then used as a lubricant additive in polyalkylene glycol (PAG).     

A novel ultrasensitive surface plasmon resonance-based nanosensor for nitrite detection

Nitrite is a common food additive, however, its reduction product, nitrosamine, is a strong carcinogen, and hence the ultra-sensitive detection of nitrite is an effective means to prevent related cancers. In this study, different sized gold nanoparticles (AuNPs) were modified with P-aminothiophenol (ATP) and naphthylethylenediamine (NED). In the presence of nitrite, satellite-like AuNPs aggregates formed via the diazotization coupling reaction and the color of the system was changed by the functionalized AuNPs aggregates. The carcinogenic nitrite content could be detected by colorimetry according to the change in the system color. The linear concentration range of sodium nitrite was 0–1.0 μg mL⁻¹ and the detection limit was determined to be 3.0 ng mL⁻¹. Compared with the traditional method, this method has the advantages of high sensitivity, low detection limit, good selectivity and can significantly lower the naked-eye detection limit to 3.0 ng mL⁻¹. In addition, this method is suitable for the determination of nitrite in various foods. We think this novel designed highly sensitive nitrate nanosensor holds great market potential.

A satellite-like AuNP aggregate-based nitrite detection nanosensor was designed via diazotization coupling reaction and can significantly lower the naked-eye detection limit to 3.0 ng mL⁻¹. This nanosensor has important applications in food detection and cancer prevention.     

Facile solvothermal synthesis of nitrogen-doped SnO2 nanorods towards enhanced photocatalysis

Heteroatom doping has proved to be one of the most effective approaches to further improve the photocatalytic activities of semiconducting oxides originating from the modulation of their electronic structures. Herein, nitrogen-doped SnO₂ nanorods were synthesized via facile solvothermal processes using polyvinylpyrrolidone (PVP) as a dispersing agent and ammonium water as the N source, respectively. Compared with pure SnO₂ sample, the as-synthesized nitrogen-doped SnO₂ nanorods demonstrated enhanced photocatalytic performances, evaluated by the degradation of rhodamine B (RhB), revealing the effectiveness of nitrogen doping towards photocatalysis. In particular, the optimal photocatalyst (using 0.6 g PVP and 1 mL ammonia water) could achieve up to 86.23% pollutant removal efficiency under ultraviolet (UV) light irradiation within 150 min, showing 17.78% higher efficiency than pure SnO₂. Detailed structural and spectroscopic characterization reveals the origin of activity enhancement of nitrogen-doping SnO₂ in contrast with pure SnO₂. Specifically, the bandgap and the morphologies of nitrogen-doped SnO₂ have changed with more chemisorbed sites, which is supposed to result in the enhancement of photocatalytic efficiency. Moreover, the possible formation mechanism of nitrogen-doped SnO₂ nanorods was discussed, in which PVP played a crucial role as the structure orientator.

Nitrogen-doped SnO₂ nanorods were synthesized via facile solvothermal processes, which demonstrated enhanced photocatalytic performances evaluated by the degradation of rhodamine B (RhB), revealing the effectiveness of nitrogen doping towards photocatalysis.