Self-Assembly-Directed Aerogel and Membrane Formation from a Magnetic Composite: An Approach to Developing Multifunctional Materials

Herein, we report the preparation of an aerogel and a membrane from a magnetic composite material by tuning the self-assembly at the molecular level. The gel exhibits an excellent oil absorption property, and the membrane shows a remarkable autonomous self-healing property. The composite is formed from an organosilicon-modified poly­(amidoamine) (PAMAM) dendrimer, which is linked with iron oxide nanoparticles and poly­(vinyl alcohol). Upon the addition of a cross-linker (formaldehyde), the system undergoes a fast self-assembly and gelation process. The aerogel, obtained after drying of the hydrogel, was modified with 1- bromohexadecane at room temperature and utilized for the removal of oil from water with 22.9 g/g absorption capacity. Intriguingly, the same system forms a membrane with 97% autonomous self-healing ability, in the absence of the cross-linker. The membrane was used to remove the salt content from water with an efficiency of 85%. The control experiments suggest that the presence of the magnetic material (iron oxide) plays a key role in the formation of both the aerogel and membrane

Sunlight Induced Synthesis of Reversible and Reusable Biocapped Nanoparticles for Metal Ion Detection and SERS Studies

The present work describes an eco-friendly synthesis of silver and gold nanoparticles using an aqueous extract of the bone powder of a dry marine organism (seahorse), which acts both as a reducing as well as stabilizing agent. The novel photoinduced formation of the nanoparticles (NPs) was characterized by UV–vis absorption, dynamic light scattering, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) experiments. The role of pH on the feasibility of nanoparticle formation has been investigated. The results suggest that photoinduced electron transfer from the amino acids present in the bone extract is responsible for the reduction of the nanoparticle precursors. The as-synthesized nanoparticles have been utilized as “naked eye” sensors for the detection of multiple ions (Cu²⁺, Cr³⁺, V⁴⁺, and UO₂²⁺) at <i>micromolar</i> concentration of the analytes. Furthermore, the NPs were found to enhance the surface Raman peaks from dye molecule (rhodamine 6G) at <i>nanomolar</i> concentration of the analyte. More significantly, a novel and efficient sunlight induced reversible aggregation pathway for the as-synthesized nanoparticles has been demonstrated

Charge Transfer Modulated Self-Assembly in Poly(aryl ether) Dendron Derivatives with Improved Stability and Transport Characteristics

Alteration of native gelation properties of anthracene and pyrene cored first generation poly­(aryl ether) dendrons, G1-An and G1-Py, by introducing a common acceptor, 2,4,7-trinitro-9<i>H</i>-fluoren-9-one (TNF), results in forming charge transfer gels in long chain alcoholic solvents. This strategy leads to significant perturbation of optical and electronic properties within the gel matrix. Consequently, a noticeable increase of their electrical conductivities is observed, making these poly­(aryl ether) dendron based gels potential candidates for organic electronics. While the dc-conductivity (σ) value for the native gel from G1-An is 2.8 × 10^–4 S m^–1, the value increased 3 times (σ = 8.7 × 10^–4 S m^–1) for its corresponding charge transfer gel. Further, the dc-conductivity for the native gel self-assembled from G1-Py dramatically enhanced by approximately an order of magnitude from 4.9 × 10^–4 to 1.3 × 10^–3 S m^–1, under the influence of an acceptor. Apart from H-bonding and π···π interactions, charge transfer results in the formation of a robust 3D network of fibers, with improved aspect ratio, providing high thermo-mechanical stability to the gels compared to the native ones. The charge transfer gels self-assembled from G1-An/TNF (1:1) and G1-Py/TNF exhibit a 7.3- and 2.5-fold increase in their yield stress, respectively, compared to their native assemblies. A similar trend follows in the case of their thermal stabilities. This is attributed to the typical bilayer self-assembly of the former which is not present in the case of G1-Py/TNF charge transfer gel. Density functional calculations provide deeper insights accounting for the role of charge transfer interactions in the mode of self-assembly. The 1D potential energy surface for the G1-An/TNF dimer and G1-Py/TNF dimer is found to be 11.8 and 1.9 kcal mol^–1 more stable than their corresponding native gel dimers, G1-An/G1-An and G1-Py/G1-Py, respectively

Tunable Morphology and Mesophase Formation by Naphthalene-Containing Poly(aryl ether) Dendron-Based Low-Molecular-Weight Fluorescent Gels

Novel poly­(aryl ether) dendron-based low-molecular-weight organogelaters (LMWG) containing naphthalene units at the core have been synthesized, and the self-assembly of the system has been examined in a variety of solvents and solvent mixtures. The compounds readily form gels with attractive critical gel concentration values associated with gelation-induced enhanced emission (GIEE). In addition to the remarkable properties of the previously reported anthracene and pyrene analogues (Rajamalli, P.; Prasad, E. <i>Org. Lett.</i> <b>2011</b>, <i>13,</i> 3714 and Rajamalli, P.; Prasad, E. <i>Soft Matter</i> <b>2012</b>, <i>8,</i> 8896), the self-assembled systems exhibit distinctly different structure–property relationships. Unlike the reported ones, the present system forms sheetlike morphology in nonpolar solvent mixtures, giant vesicles in polar solvent mixtures, and lamellar or hexagonal columnar phases in single solvents. The unique properties of the self-assembled systems, which were analyzed through electron microscopic (SEM, TEM, AFM) and spectroscopic techniques (POM, fluorescence), are attributed to the replacement of anthracene/pyrene units by naphthalene units. The present work unravels the subtle role of minute structural change in altering the properties of LMWGs based on poly­(aryl ether) dendrons

White-Light Emission from Unmodified Graphene Oxide Quantum Dots

We report herein the synthesis and characterization of unmodified graphene oxide quantum dots (GOQDs) with white-light-emitting properties, upon photoexcitation at 340 nm. The Commission International de l’Éclairage (CIE) 1931 chromaticity coordinates for GOQDs (<i>x</i> = 0.29, <i>y</i> = 0.34) suggest that highly pure white-light emission was achieved. A detailed mechanistic study was carried out utilizing UV–visible absorption, steady-state and time-resolved fluorescence spectroscopy, and dynamic light scattering (DLS) techniques to understand the origin of the white-light emission. The results taken together suggest that GOQDs could self-assemble in solution and thus transform the luminescence behavior. Furthermore, the results indicate that the pH of the medium also plays a crucial role in assisting the aggregation to generate the white-light emission. The concentration-dependent DLS measurements support a cooperative mechanism for the aggregation kinetics in the system. More importantly, the study suggests that white-light emission can be generated from unmodified graphene oxide quantum dots by tuning their nanoscopic aggregation properties

Visual and Optical Sensing of Hg²⁺, Cd²⁺, Cu²⁺, and Pb²⁺ in Water and Its Beneficiation via Gettering in Nanoamalgam Form

A “turn on” fluorescent probe based on denatured bovine serum albumin (BSA)–Pyronin Y complex (PYdBSA) has been prepared using a one pot approach. This probe can detect nanomolar concentrations of common contaminant ions (Hg²⁺, Cd²⁺, Cu²⁺, and Pb²⁺) found in wastewater. The probe shows the highest fluorescence response for Hg²⁺ (relative intensity set to 100%) and a very good response for Cd²⁺ (60%), Cu²⁺ (50%), and Pb²⁺ (20%). The probe is water-soluble and has photo excitation in the visible region (530 nm). More interestingly, the presence of the contaminant ions under consideration can be visually detected due to the distinct color formation upon addition of the analytes in micromolar (1 μM) concentrations. The limit of detection (LOD) with fluorometry is 9 nM for Hg²⁺ (<2 ppb; consistent with standards given by the U.S. Environmental Protection Agency). This probe signal is found to be intact even in the presence of other metal ions such as Zn²⁺, Co²⁺, Fe²⁺, Ag⁺, K⁺, Na⁺, Al³⁺, Ca²⁺, Fe³⁺, Ni²⁺, Sb³⁺, and Mg²⁺, which is rationalized using hard–soft acid–base theory. Postdetection, the heavy and transition metals (HTMs) are gettered in the form of nanoamalgam through reduction using sodium borohydride. The nanomaterials obtained are rationalized based on known phase fields in relevant binary phase diagrams. The nanoaluminum amalgam obtained is beneficiated by putting it in use as a reducing agent in the conversion of <i>p</i>-nitrophenol to <i>p</i>-aminophenol. The rate constant (0.74 ± 0.08 M^–1 s^–1) obtained is comparable to the best reducing agents reported for this reaction. Hence, we demonstrate the practical relevance of the reported method for detection, gettering, and beneficiation of HTMs

Rate and Mechanistic Investigation of Eu(OTf)₂‑Mediated Reduction of Graphene Oxide at Room Temperature

We describe a fast, efficient, and mild approach to prepare chemically reduced graphene oxide (rGO) at room temperature using divalent europium triflate {Eu­(OTf)₂}. The characterization of solution-processable reduced graphene oxide has been carried out by various spectroscopic (FT-IR, UV–visible absorption, and Raman), microscopic (TEM and AFM), and powder X-ray diffraction (XRD) techniques. Kinetic study indicates that the bimolecular rate constants for the reduction of graphene oxide are 13.7 ± 0.7 and 5.3 ± 0.1 M^–1 s^–1 in tetrahydrofuran (THF)–water and acetonitrile (ACN)–water mixtures, respectively. The reduction rate constants are <i>two orders</i> of magnitude higher compared to the values obtained in the case of commonly used reducing agents such as the hydrazine derivative, sodium borohydride, and a glucose–ammonia mixture. The present work introduces a feasible reduction process for preparing reduced graphene oxide at ambient conditions, which is important for bulk production of GO. More importantly, the study explores the possibilities of utilizing the unique chemistry of divalent lanthanide complexes for chemical modifications of graphene oxide

Enhanced Resonance Energy Transfer and White-Light Emission from Organic Fluorophores and Lanthanides in Dendron-based Hybrid Hydrogel

In this paper, we have investigated the use of poly­(aryl ether) dendron-based gel as a medium for resonance energy transfer (RET) from organic donors (phenanthrene, naphthalene, and pyrene) to lanthanide [Eu­(III) and Tb­(III)] ions. The gel has been prepared through self-assembly of glucose-cored poly­(aryl ether) dendrons in a dimethyl sulfoxide/water mixture (1:9 v/v). The efficiency of RET was calculated by metal-centered emission quantum yield measurements in the gel medium. While there was no resonance energy transfer observed between the donor–acceptor pairs in solution, efficient RET has been observed in the gel medium. The metal-centered quantum yield values were 11.9% for phenanthrene–Eu­(III), 3.9% for naphthalene–Eu­(III), and 3.6% for pyrene–Eu­(III) systems. Partial RET in the system has been utilized to generate white-light emission from the gel by incorporating an additional lanthanide ion, Tb­(III), along with the organic donors and Eu­(III). The CIE (Commission Internationale d’Eclairage) coordinates obtained for gels formed by phenanthrene–Tb­(III)–Eu­(III) (PTE), naphthalene–Tb­(III)–Eu­(III) (NTE), and pyrene–Tb­(III)–Eu­(III) (PyTE) were (0.33, 0.32) for PTE, (0.35, 0.37) for NTE, and (0.35, 0.33) for PyTE. The correlated color temperatures (CCT) for white-light-emitting gels were calculated, and the values (5520 K for PTE, 4886 K for NTE, and 4722 K for PyTE) suggest that the system generates cool white light

A Gelation-Induced Enhanced Emission Active Stimuli Responsive and Superhydrophobic Organogelator: “Turn-On” Fluorogenic Detection of Cyanide and Dual-Channel Sensing of Nitroexplosives on Multiple Platforms

A pyrene-based highly emissive low-molecular-weight organogelator, [2-(4-fluorophenyl)-3-(pyren-1-yl)acrylonitrile] (F1), is presented, which divulges thixotropic and thermochromic fluorescence switching via reversible gel-to-sol transition and tremendous superhydrophobicity (mean contact angles: 149–160°), devoid of any gelling and/or hydrophobic units. The rationale for the design strategy reveals that the restricted intramolecular rotation (RIR) in J-type self-assembly promotes F1 for the prolific effects of aggregation- and gelation-induced enhanced emission (AIEE and GIEE). Meanwhile, hindrance in charge transfer via the nucleophilic reaction of cyanide (CN–) on the CC unit in F1 facilitates the selective fluorescence “turn-on” response in both solution [9:1 (v/v) DMSO/water] and solid state [paper kits] with significantly lower detection limits (DLs) of 37.23 nM and 13.4 pg/cm2, respectively. Subsequently, F1 discloses CN– modulated colorimetric and fluorescence “turn-off” dual-channel response for aqueous 2,4,6-trinitrophenol (PA) and 2,4-dinitrophenol (DNP) in both solution (DL = 49.98 and 44.1 nM) and solid state (DL = 114.5 and 92.05 fg/cm2). Furthermore, the fluorescent nanoaggregates of F1 in water and its xerogel films permit a rapid dual-channel “on-site” detection of PA and DNP, where the DLs ranged from nanomolar (nM) to sub-femtogram (fg) levels. Mechanistic insights reveal that the ground-state electron transfer from the fluorescent [F1-CN] ensemble to the analytes is responsible for anion driven sensory response, whereas the unusual inner filter effect (IFE) driven photoinduced electron transfer (PET) was responsible for self-assembled F1 response toward desired analytes. Additionally, the nanoaggregates and xerogel films also detect PA and DNP in their vapor phase with reasonable percentage of recovery from the soil and river water samples. Therefore, the elegant multifunctionality from a single luminogenic framework allows F1 to provide a smart pathway for achieving environmentally benign real-world applications on multiple platforms

Diffusion of Solvent-Separated Ion Pairs Controls Back Electron Transfer Rate in Graphene Quantum Dots

In the present study, the stability of the photogenerated, solvent-separated charged states of graphene quantum dots (GQDs) in the presence of <i>N</i>,<i>N</i>-diethylaniline (DEA) has been evaluated in a series of organic solvents. The results indicate that the rate constant for back electron transfer (<i>k</i>_BET) from GQD radical anion to DEA radical cation is diffusion-controlled. As a result of the diffusion-controlled back electron transfer (BET), <i>k</i>_BET exhibits an inverse exponential relation to (a) the viscosity coefficient (η) of the solvent and (b) the average radius of the graphene quantum dots. An analytical expression for the diffusion-controlled back electron transfer rate constant has been formulated. The dependence of <i>k</i>_BET on the diffusion of solvent-separated ion pairs has been evaluated for the first time for quantum dot systems and the results provide an efficient method for enhancing the lifetime of the photogenerated charge-separated states from graphene quantum dots. The present findings can potentially improve the performance of GQD-based photovoltaic and optoelectronic devices