Gold Nanoplate-Based 3D Hierarchical Microparticles: A Single Particle with High Surface-Enhanced Raman Scattering Enhancement

Formation of intended nano- and microstructures with regular building blocks has attracted much attention because of their potential applications in the fields of optics, electronics, and catalysis. Herein, we report a novel strategy to spontaneously grow three-dimensional (3D) hierarchical cabbagelike microparticles (CLMPs) constructed by individual Au nanoplates. By reducing gold precursor to gold atoms, <i>N</i>-(3-amidino)-aniline (NAAN) itself was oxidized to form poly­(<i>N</i>-(3-amidino)-aniline) (PNAAN), which specifically binds on Au(111) facet as a capping agent and which leads to the formation of gold nanoplates. Because of the incomplete coverage of Au(111) facet, new gold nanoplate growth sites were spontaneously generated from the crystal plane of existing Au nanoplates for the growth of other nanoplates. This process continued until the nanoplate density reached its maximum range, eventually resulting in CLMPs with well-controlled structures. This opens a new avenue to utilize the imperfection during nanoparticle (NP) growth for the construction of microstructures. The individual CLMP shows excellent surface-enhanced Raman scattering (SERS) performance with high enhancement factor (EF) and good reproducibility as it integrates the SERS enhancement effects of individual Au nanoplate and the nanogaps formed by the uniform and hierarchical structures

Formation and Self-assembly of Gold Nanoplates through an Interfacial Reaction for Surface-Enhanced Raman Scattering

3D hierarchical architectures assembled from individual particles have attracted great interest because they displayed novel properties from the individual building blocks as well as their complex structures. Here we present a new strategy to form 3D hierarchical gold (Au) nanostructures via an interfacial reduction reaction. An aniline (ANI) derivative, N-(3-amidino)-aniline (NAAN), and HAuCl₄ were separately dissolved in toluene and water to form an organic/water interface. Au nanoplates formed at the interface and subsequently moved to the aqueous phase. As a capping agent for the nanoplate formation, the oxidized NAAN, i.e., poly­(N-(3-amidino)-aniline) (PNAAN), also facilitated the self-assembly of Au nanoplates into 3D hierarchical Au nanoflowers (AuNFs) through π–π stacking. The individual AuNF exhibited good surface-enhanced Raman scattering (SERS) response both in enhancement factor and reproducibility because it integrates the SERS enhancement effects of individual Au nanoplates and their hierarchical structures. This is the first report depicting the one-pot formation and self-assembly of Au nanoplates into 3D organized hierarchical nanostructures through the molecular interaction of conducting polymer

Detection of Dissolved CO₂ Based on the Aggregation of Gold Nanoparticles

A sensitive colorimetric assay of dissolved CO₂ (dCO₂) was developed based on the plasmon shift of gold nanoparticles (AuNPs). A water-soluble random copolymer poly­(dimethyl acrylamide-co-(<i>N</i>-amidino)­ethyl acrylamide), or P­(DMA-co-NAEAA), containing amidine groups was synthesized. In the presence of dCO₂, the amidine groups in the NAEAA block protonate and convert the polymer from a neutral to a positive-charged state, hence triggering the negative-charged AuNPs to aggregate by the electrostatic interaction. The degree of AuNP aggregation is dependent on the charge density of polymer, which is related to dCO₂ concentration. The aggregation of AuNPs results in a red shift of the AuNP plasmonic spectrum, or a color change from red to blue. In addition, dCO₂ concentration can be quantitatively measured by the UV absorbance change of the AuNP solution. A linear relationship between 0.264 and 6.336 hPa of dCO₂ with a limit of detection (LOD) of 0.04 hPa can be acquired. This is the first report to detect dCO₂ using the optical properties of nanoparticles

Reversible Actuation of Polyelectrolyte Films: Expansion-Induced Mechanical Force Enables <i>cis–trans</i> Isomerization of Azobenzenes

Fabrication of light-driven actuators that can prolong their deformation without constant irradiation poses a challenge. This study shows the preparation of polymeric actuators that are capable of reversible bending/unbending movements and prolonging their bending deformation without UV irradiation by releasing thermally cross-linked azobenzene-containing polyelectrolyte films with a limited free volume from substrates. Layer-by-layer assembly of poly­{1–4­[4-(3-carboxy-4-hydroxyphenylazo)­benzenesulfonamido]-1,2-ethanediyl sodium salt} (PAZO)–poly­(acrylic acid) (PAA) complexes (noted as PAZO–PAA) with poly­(allylamine hydrochloride) (PAH) produces azobenzene-containing PAZO–PAA/PAH films. UV irradiation induces <i>trans–cis</i> isomerization of azobenzenes and allows large-scale bending deformation of the actuators. The actuators prolong the bending deformation even under visible light irradiation because the <i>cis–trans</i> back isomerization of azobenzenes is inhibited by the limited free volume in the actuators. Unbending of actuators is attained by exposing the actuators to a humid environment at room temperature. Film expansion in a humid environment produces a mechanical force that is sufficiently strong to enable the <i>cis–trans</i> back isomerization of azobenzenes and restore the bent actuators to their original configuration. The capability of the force produced by film expansion for <i>cis–trans</i> azobenzene isomerization can be helpful for designing novel polymeric actuators

CO₂‑Responsive Polymer-Functionalized Au Nanoparticles for CO₂ Sensor

Metallic nanoparticles (NPs) coated with stimuli-responsive polymers (SRPs) exhibit tunable optical properties responding to external stimuli and show promising sensing applications. We present a new CO₂-responsive polymer, poly­(<i>N</i>-(3-amidino)-aniline) (PNAAN), coated gold NPs (AuNPs) synthesized by directly reducing HAuCl₄ with a CO₂-responsive monomer <i>N</i>-(3-amidino)-aniline (NAAN). The amidine group of PNAAN can be protonated into a hydrophilic amidinium group by dissolved CO₂ (dCO₂). This induces the PNAAN to swell and detach from the AuNP surface, resulting in AuNP aggregation and color change. By monitoring the UV absorbance change of AuNPs, a sensitive dCO₂ sensor with a linear range of 0.0132 to 0.1584 hPa and a limit of detection (LOD) of 0.0024 hPa is developed. This method shows dramatic improvement in sensitivity and convenience of sample preparation compared with the previously reported dCO₂ sensor

Chemical Sensing on a Single SERS Particle

We report a new chemical sensing platform on a single surface-enhanced Raman scattering (SERS) particle. A cabbage-like Au microparticle (CLMP) with high SERS enhancement was applied as an ultrasensitive SERS substrate. A new Raman reporter bis­[4,4′-[dithiodiphenyl azo-phenol] (DTDPAP) was synthesized to display multiple fingerprints and high reactivity toward sodium dithionite. The reaction of DTDPAP with sodium dithionite was in situ monitored by SERS on a single CLMP. The DTDPAP fingerprint change is dependent on the sodium dithionite concentration, providing a simple and sensitive method for sodium dithionite profiling

Reversible Actuation of Polyelectrolyte Films: Expansion-Induced Mechanical Force Enables <i>cis–trans</i> Isomerization of Azobenzenes

Fabrication of light-driven actuators that can prolong their deformation without constant irradiation poses a challenge. This study shows the preparation of polymeric actuators that are capable of reversible bending/unbending movements and prolonging their bending deformation without UV irradiation by releasing thermally cross-linked azobenzene-containing polyelectrolyte films with a limited free volume from substrates. Layer-by-layer assembly of poly­{1–4­[4-(3-carboxy-4-hydroxyphenylazo)­benzenesulfonamido]-1,2-ethanediyl sodium salt} (PAZO)–poly­(acrylic acid) (PAA) complexes (noted as PAZO–PAA) with poly­(allylamine hydrochloride) (PAH) produces azobenzene-containing PAZO–PAA/PAH films. UV irradiation induces <i>trans–cis</i> isomerization of azobenzenes and allows large-scale bending deformation of the actuators. The actuators prolong the bending deformation even under visible light irradiation because the <i>cis–trans</i> back isomerization of azobenzenes is inhibited by the limited free volume in the actuators. Unbending of actuators is attained by exposing the actuators to a humid environment at room temperature. Film expansion in a humid environment produces a mechanical force that is sufficiently strong to enable the <i>cis–trans</i> back isomerization of azobenzenes and restore the bent actuators to their original configuration. The capability of the force produced by film expansion for <i>cis–trans</i> azobenzene isomerization can be helpful for designing novel polymeric actuators

Corrosion Behavior of Metallic Materials in Acidic-Functionalized Ionic Liquids

This paper describes the influence of temperature, water content, and anionic type of acidic-functionalized ionic liquids (ILs), 1-(4-sulfobutyl)-3-methylimidazolium hydrogen sulfate ([BsMIM]­[HSO₄]) and 1-(4-sulfobutyl)-3-methylimidazolium toluenesulfonate ([BsMIM]­[OTs]), on the corrosion behavior of Fe, Ni, and 304 stainless steel (304SS). Electrochemical methods including electrochemical impedance spectroscopy (EIS) and Tafel plots were used to investigate it. Also, scanning electron microscopy (SEM) was used to characterize the nature of the corrosion morphology. The obtained electrochemical results indicated that increasing temperature accelerates the corrosion, while decreasing IL concentration retards the corrosion. The corrosion process is controlled by charge transfer. Moreover, the bisulfate anion (HSO₄^–) has an effect on the corrosion rate more significantly than the <i>p</i>-toluenesulfonate anion (OTs^–) does. The SEM spectrum showed that the corrosion situation of Fe is more serious than Ni and 304SS performed in IL-based solutions, especially in [BsMIM]­[HSO₄]. Also, the protective layer formed on the 304SS surface is more uniform. On the basis of these consistent finds, the corrosion mechanism is assumed

A new 1-D chain based on the trivacant monocapped Keggin arsenomolybdate and the copper complex linker: synthesis, crystal structure, and ESI-MS analyses

<div><p>A new organic–inorganic hybrid (H₂en)₂[[Cu(en)₂]As^IIIAs^VMo^VI₉O₃₄]·6H₂O (<b>1</b>), containing a 1-D helical chain based on the trivacant monocapped Keggin arsenomolybdate and the copper complex linker {[Cu(en)₂][As^IIIAs^VMo^VI₉O₃₄]}_n⁴ⁿ⁻ (en = ethylenediamine), has been synthesized and characterized by IR spectra, TG analyses, single-crystal X-ray diffraction, and high-resolution electrospray ionization mass spectrometry (ESI-MS). Large voids are observed and a 1-D chain containing repeated (H₂O)₈ water units from lattice water molecules is formed along the <i>a</i> axis in the crystal structure. The high-resolution ESI-MS shows that the intact framework [Cu(en)₂][As^IIIAs^VMo^VI₉O₃₄]⁴⁻ exists in solution.</p></div

Modulating Dimensionality of 2D Perovskite Layers for Efficient and Stable 2D/3D Perovskite Photodetectors

Two-dimensional (2D) perovskites have been widely adopted for improving the performance and stability of three-dimensional (3D) metal halide perovskite devices. However, rational manipulation of the phase composition of 2D perovskites for suitable energy level alignment in 2D/3D perovskite photodetectors (PDs) has been rarely explored. Herein, we precisely controlled the dimensionality of the 2D perovskite on CsPbI2Br films by tuning the polarity of the n-butylammonium iodide (BAI)-based solvents. In comparison to the pure n = 1 2D perovskite (ACN-BAI) formed by acetonitrile treatment, a mixture of n = 1 and n = 2 phases (IPA-BAI) generated by isopropanol (IPA) treatment guaranteed more robust defect passivation and favorable energy level alignment at the perovskite/hole transport layer interface. Consequently, the IPA-BAI PD exhibited a responsivity of 0.41 A W–1, a detectivity of 1.01 × 1013 Jones, and a linear dynamic range of 120 dB. Furthermore, the mixed-phase 2D layer effectively shielded the 3D perovskite from moisture. The IPA-BAI device retained 76% of its initial responsivity after 500 h of nonencapsulated storage at 10% relative humidity. This research provides valuable insights into the dimensional modulation of 2D perovskites for further enhancing the performance of 2D/3D perovskite PDs