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The possibility of converting waste plastics into carbon dots (CDs) with 100% efficiencies using KMnO4 has emerged as a significant discovery in mitigating plastic pollution and upcycling. However, the lack of tunability of their properties, viz. aerial O2 harvesting, light-induced autophagy, and photoactivity using air as a free oxidant, has remained a bottleneck. Besides, the toxicity of KMnO4 makes the process less sustainable. Attempting to bridge these gaps, herein, we demonstrate the preparation of CDs using polyethylene with enormous controllability of their properties by utilizing less-toxic and metal-residue-free oxidizers, e.g., H2O2, HNO3, HClO4, and NaClO. We obtain structurally diverse CDs with controllable luminescent quantum yields (â¼0.5-8%), excitonic lifetimes (1.3-2.3 ns), and binding energies (147-290 meV). These CDs exhibit a hugely extended range of molecular O2 harvesting (â¼405-650 µM) with different amounts of strongly and weakly surface-bound O2 molecules within an estimated ratio of â¼0.77-2.51. Autophagy varied from 14 days to a nearly "no-autophagy" show. We efficiently utilized their oxygen harvesting and photocatalytic abilities to synthesize imine compounds from the corresponding amines in the open air (rate constant of â¼0.055 min-1), surpassing the literature efficiencies achieved using an O2 flow and noble metals. Notably, due to oxygen harvesting by CDs, no additional rate enhancement was observed after O2 purging, establishing the role of CDs in making free air an excellent oxidizing agent.
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The precise sequence of a protein's primary structure is essential in determining its folding pathways. To emulate the complexity of these biomolecules, functional block copolymers consisting of segmented triblocks with distinct functionalities positioned in a sequence-specific manner are designed to control the polymer chain compaction. Triblock polymers P- b -C- b -F and P- b -F- b -C and random diblock copolymer P- b -C- r -F consist of a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic block with coumarin (C) and ferrocene (F) moieties that are grafted in a sequence-specific or random manner onto the hydrophilic block. External stimuli such as UVB light, redox, and chemical cues influence the functional hydrophobic block to alter the packing parameters that are monitored with spectroscopic and scattering techniques. Interestingly, the positioning of the stimuli-responsive moiety within the hydrophobic block of P- b -C- b -F, P- b -F- b -C, and P- b -C- r -F affects the extent of the hydrophobic-hydrophilic balance in block copolymers that renders orthogonal control in stimuli-responsive transformation of self-assembled vesicles to micelles.
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Modern technology demands miniaturization of electronic components to build small, light, and portable devices. Hence, discovery and synthesis of new non-toxic, low cost, ultra-thin ferroelectric materials having potential applications in various electronic and optoelectronic devices are of paramount importance. However, achieving room-temperature ferroelectricity in two dimensional (2D) ultra-thin systems remains a major challenge as conventional three-dimensional ferroelectric materials lose their ferroelectricity when the thickness is brought down below a critical value owing to the depolarization field. Herein, we report room-temperature ferroelectricity in ultra-thin single-crystalline 2D nanosheets of Bi2O2S synthesized by a simple, rapid, and scalable solution-based soft chemistry method. The ferroelectric ground state of Bi2O2S nanosheets is confirmed by temperature-dependent dielectric measurements as well as piezoelectric force microscopy and spectroscopy. High resolution transmission electron microscopy analysis and density functional theory-based calculations suggest that the ferroelectricity in Bi2O2S nanosheets arises due to the local distortion of Bi2O2 layers, which destroys the local inversion symmetry of Bi2O2S.
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Achieving a high electrocatalytic performance using a completely metal-free electrocatalyst, preferably based on only carbonaceous materials, remains a challenge. Alternatively, an efficient composite of a carbon nanostructure and a non-noble metal with minimum dependence on a metal holds immense potential. Although single-atom catalysis brings superior performance, its complex synthetic strategy limits its large-scale implementation. Previous investigation has shown that atomic dispersion (Fe-Nx-C) is accompanied by higher metal-loss compared to nanoparticle formation (Fe-NPs-N-C). Therefore, to achieve minimum metal loss, we first incorporated iron nanoparticles (Fe NPs) to N-doped carbon (N-C) and then exposed them to a cheap carbon source, melamine at high temperature, resulting in the growth of carbon nanotubes (CNTs) catalysed by those Fe NPs loaded on N-C (Fe-NPs-N-C). Thermogravimetric analysis showed that the metal-retention in the composite is higher than that in the bare carbon nanotube and even the atomically dispersed Fe-active sites on N-C. The composite material (Fe-NPs-N-C/CNT) shows a high half-wave potential (0.89 V vs. RHE) which is superior to that of commercial Pt/C towards the oxygen reduction reaction (ORR). The enhanced activity is attributed to the synergistic effect of high conductivity of CNTs and active Fe-sites as the composite exceeds the individual electrocatalytic performance shown by Fe-CNTs & Fe-NPs-N-C, and even that of atomically dispersed Fe-active sites on N-C.
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Clean water is a fundamental human right but millions struggle for it daily. Herein, we demonstrate a new piezo-photocatalyst with immense structural diversity for universal wastewater decontamination. Single-crystalline Bi4TaO8Cl nanoplates with exposed piezoelectric facets exhibit visible-light response, piezoelectric behavior with coercive voltages of ±5 V yielding 0.35% crystal deformation, and pressure-induced band-bending of >2.5 eV. Using five common contaminants of textile and pharmaceutical industries, we show that the nanoplates can mineralize them in all piezocatalytic, photocatalytic, and piezo-photocatalytic approaches with efficiencies higher than most catalysts developed for just one contaminant. Their efficiencies for feedstocks differing over 2 orders of magnitude in concentrations, the highest to date, are also demonstrated to simulate real-life situations. These extensive studies established that combining piezocatalytic and photocatalytic approaches can lead to a tremendous synergy exceeding >45%. The origin of synergy has been illustrated for the first time using band-bending models and improved charge transfer from valence and conduction band electronic surfaces. We further quantified synergy across reactants, concentrations, and ultrasonic frequency and power to demonstrate their versatility and unpredictability. Finally, seven parameters that contribute to synergy but create unpredictability have been identified for the rational design of piezo-photocatalysts for wastewater treatment.
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Piezocatalytic water splitting is an emerging approach to generate "green hydrogen" that can address several drawbacks of photocatalytic and electrocatalytic approaches. However, existing piezocatalysts are few and with minimal structural flexibility for engineering properties. Moreover, the scope of utilizing unprocessed water is yet unknown and may widely differ from competing techniques due to the constantly varying nature of surface potential. Herein, we present Bi4TaO8Cl as a representative of a class of layered perovskite oxyhalide piezocatalysts with high hydrogen production efficiency and exciting tailorable features including the layer number, multiple cation-anion combination options, etc. In the absence of any cocatalyst and scavenger, an ultrahigh production rate is achievable (1.5 mmol g-1 h-1), along with simultaneous generation of value-added H2O2. The production rate using seawater is somewhat less yet appreciably superior to photocatalytic H2 production by most oxides as well as piezocatalysts and has been illustrated using a double-layer model for further development.
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Designing intimate interfacial contact between nanostructures and two-dimensional (2D) materials is highly desirable to influence the movement of generated charge carriers. Nanostructured zinc oxide (ZnO) is a fascinating material with unique optical and electrical properties. 2D reduced graphene oxide (rGO) exhibits semiconductor behaviour with tunable catalytic activity and excellent biocompatibility. Hence, we have designed a hybrid material by selecting nanostructures of an oxide semiconductor (ZnO) with reduced graphene oxide (rGO) using a hard integration technique followed by a low-temperature hydrothermal route. The good encapsulation of rGO over the ZnO nanorods was confirmed by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The photocatalytic activities of ZnO, rGO, and ZnO/rGO were studied under visible-light irradiation using three different toxic dyes, methylene blue (MB), methyl orange (MO), and Congo red (CR). The composite materials exhibited excellent efficiencies of 100, 95, and 90% for the degradation of MB, MO, and CR, respectively. Moreover, the degradation of the dye was found to follow first-order kinetics. The enhanced efficiencies are attributed to the adsorption and efficient charge transfer from rGO to the conduction band of ZnO. The role of the multifunctional facets of graphene was presented to elucidate the visible-light activity of the composite materials for enhanced efficiency. The main reactive species (e-) of the reduction reaction were confirmed through a radical trapping experiment, which showed the generation of highly reactive â¢OH radicals that decompose the toxic dye. The results provide a perspective for developing graphene-based composite materials with desired preselected nanostructures for solar energy utilisation.
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Grafito , Nanoestructuras , Óxido de Zinc , Catálisis , Colorantes , Rojo Congo , Grafito/química , Azul de Metileno/química , Nanoestructuras/química , Óxido de Zinc/químicaRESUMEN
Insights into developing innovative routes for the stabilization of photogenerated charge-separated states by suppressing charge recombination in photocatalysts is a topic of immense importance. Herein, we report the synthesis of a metal-organic framework (MOF)-based composite where CdS nanoparticles (NPs) are confined inside the nanosized pores of Zr4+-based MOF-808, namely, CdS@MOF-808. Anchoring l-cysteine into the nanospace of MOF-808 via postsynthetic ligand exchange allows the capture of Cd2+ ions from their aqueous solution, which are further utilized for in situ growth of CdS NPs inside the nanosized MOF pores. The formation of CdS@MOF-808 opens up a possibility for visible-light photocatalysis as CdS NPs (1-2 nm) are a well-studied semiconductor system with a band gap of â¼2.6 eV. The confinement of the CdS NPs inside the MOF pores, close to the Zr4+ cluster, opens up a shorter electron transfer route from CdS to the catalytic Zr4+ cluster and shows a high rate of H2 evolution (10.41 mmol g-1 h-1) from water with a loading of 3.56 wt % CdS. In contrast, a similar composite in which CdS NPs are stabilized on the external surface of MOF-808 reveals poor activity (0.15 mmol g-1 h-1). CdS NPs stabilized on the MOF-808 surface show slower and inefficient electron transfer kinetics compared to CdS stabilized inside the nanospace of the MOF, as realized by the transient absorption measurements. Therefore, this work unveils the critical role of stabilizing the photosensitizer NPs in close proximity of the catalytic sites in MOF systems towards developing highly efficient H2 evolution photocatalysts.
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Carbon quantum dots (CQDs) represent a class of carbon materials exhibiting photoresponse and many potential applications. Here, we present a unique property that dissolved CQDs capture large amounts of molecular oxygen from the air, the quantity of which can be controlled by light irradiation. The O2 content can be varied between a remarkable 1 wt % of the CQDs in the dark to nearly half of it under illumination, in a reversible manner. Moreover, O2 depletion enhances away from the air-solution interface as the nearby CQDs quickly regain them from the air, creating a pronounced concentration gradient in the solution. We elucidate the role of the CQD functional groups and show that excitons generated under light are responsible for their tunable adsorbed-oxygen content. Because of O2 enrichment, the photocatalytic efficiency of the CQDs toward oxidation of benzylamines in the air is the same as under oxygen flow and far higher than the existing photocatalysts. The findings should encourage the development of a new class of oxygen-enricher materials and air as a sustainable oxidant in chemical transformations.
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Even though the anion exchange membrane fuel cells have many advantages, the stability of their electrocatalysts for oxygen reduction reaction (ORR) has remained remarkably poor. We report here on the ultrathin twisty PdNi-alloy nanowires (NWs) exhibiting a very low reaction overpotential with an E1/2 â¼ 0.95 V versus RHE in alkaline media maintained over 200 K cycles, the highest ever recorded for an electrocatalyst. The mass activity of the used NWs is >10 times higher than fresh commercial Pt/C. Therein, Ni improves the Pd d-band center for a more efficient ORR, and its leaching continuously regenerates the surface active sites. The twisty nanowire morphology imparts multiple anchor points on the electrode surface to arrest their detachment or coalescence and extra stability from self-entanglement. The significance of the NW morphology was further confirmed from the high-temperature durability studies. The study demonstrates that tailoring the number of contact points to the electrode-surface may help realize commercial-grade stability in the highly active electrocatalysts.
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The present work reports the use of natural alkaline extract from coconut husk ash as a precipitating agent for metal oxide nanoparticles synthesis. The abundance of K2O and K2CO3 in it makes the extract highly basic and could be the alternative source of basic media in the laboratory. In this study, highly photoactive zinc oxide nanoparticles have been synthesized using water extract of waste coconut husk ash in a green approach which is considered as replacement of homogeneous base like NaOH and KOH. The formation of zinc oxide nanoparticles at different pH of the solution of coconut husk ash was confirmed through powder XRD, BET, SEM-EDX, UV-Vis, FTIR, and photoluminescence spectroscopy. The photocatalytic performance of the samples was evaluated through the degradation of methylene blue (MB) and methyl orange (MO) under solar irradiation which undergo degradation around 97% and 68% within 120 min, respectively. The high photocatalytic activity and rate constant could be attributed to the large surface area due to small particle size that could provide quicker photon absorption and reduction of charge carrier recombination. This current work introduces a new method to reduce energy consumption for the synthesis of highly photoactive low-cost zinc oxide nanoparticles.
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Nanopartículas del Metal , Óxido de Zinc , Catálisis , Cocos , Nanopartículas del Metal/química , Agua , Óxido de Zinc/químicaRESUMEN
The production of dynamic, environment-responsive shape-tunable biomaterials marks a significant step forward in the construction of synthetic materials that can easily rival their natural counterparts. Significant progress has been made in the self-assembly of bio-materials. However, the self-assembly of a peptide into morphologically distinct auto-fluorescent nanostructures, without the incorporation of any external moiety is still in its infancy. Hence, in this study, we have developed peptide-based self-assembled auto-fluorescent nanostructures that can shuttle between 1D and 2D morphologies. Different morphological nanostructures are well known to have varied cellular internalization efficiencies. Taking advantage of our morphologically different particles emanating from the same peptide monomer, we further explored the intracellular fate of our nanostructures. We observed that the nanostructures' cellular internalization is a complex process that gets influenced by particle morphology and this might further affect their intracellular drug delivery potential. Overall, this study provides initial cues for the preparation of environment-responsive shape-shifting peptide-nano assemblies. Efforts have also been made to understand their shape driven cellular uptake behaviour, along with establishing them as nanocarriers for the cellular delivery of therapeutic molecules.
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Nanoestructuras , Preparaciones Farmacéuticas , Colorantes , Sistemas de Liberación de Medicamentos , PéptidosRESUMEN
Nanostructures of layered materials have gained increasing attention in photocatalytic and water-treatment processes. Herein, we report on sub-30â¯nm SnS2 nanosheets (NSs) which can perform photocatalytic reduction of Cr(VI) to Cr(III) quite efficiently on one hand, while removes large quantities of toxic organic dye molecules by choosing an adsorption mode of operation over photo-degradation on the other hand, unlike most other SnS2 nanostructures. The NSs have a highly extended crystallinity growing perpendicular to the (001) lattice direction but exhibit poor X-ray diffraction for the 10â¯l (1â¯=â¯1,2,3 ) lattice planes. With such defects, the NSs have a narrow bandgap of 2.21â¯eV and exhibit a significant photocurrent density at near band-edge illumination. Cr(VI) photo-reduction using the SnS2 NSs follows a first-order reaction kinetics (rate constant of 0.10â¯min-1), five-fold higher than commercial TiO2 (P-25). Furthermore, the NSs adsorb Rhodamine B dye molecules from an aqueous solution by forming a monolayer of dye molecules following a pseudo-second-order kinetic model and exhibit an adsorption capacity ofâ¯â¼â¯53.28â¯mg/g. We show that the NSs have a Zeta potential ofâ¯â¼â¯-22â¯eV and preferably adsorb cationic dyes only. Thus the SnS2 NSs can be effective for Cr(VI) contaminated waste-water treatment in a photocatalytic manner and can also act as a potential adsorbent for polluting dye molecules either in the presence or absence of sunlight. While both these activities are known for SnS2 as well as other materials, the competitive nature of the two mechanisms while each of them is a possibility has never been investigated. Therefore, besides the high activities, the study highlights the presence of different active sites on the material surface that can respond preferentially to either inorganic or organic impurities.
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Cromo , Agua , Adsorción , ColorantesRESUMEN
We demonstrate for the first time the in-situ synthesis of Pd nanocubes (PdNC) on nitrogen-doped reduced graphene oxide (NRGO) for facile organic transformations wherein the cubic morphology of Pd can only be realized by precision-controlled acid additions in the tune of 0.02 pH variations in the reaction medium. Due to the intimate contact arising from atom-by-atom addition of Pd on NRGO, the composite has exhibited a pronounced catalyst to support charge transfer effect, shift in the d-band center, and lowering of charge-transfer resistance when compared with PdNC-NRGO ex-situ composites prepared by mixing of the preformed components of PdNC and NRGO or PdNCs alone. The activities of these catalysts were tested for the Suzuki coupling and nitroarene reduction reactions using water as an industry-friendly solvent. In both, the in-situ deposited sample exhibited substantially higher catalytic activity as well as stability when compared with an ex-situ sample or pure PdNCs. We show that a very high turnover frequency of ~31300 h-1 and ~900 h-1 are achievable by using the in-situ deposited PdNC-NRGO composite for Suzuki coupling reactions and nitroarene reduction respectively, better than the state-of-the-art catalysts developed recently, in addition to high recyclability.
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The efficient recovery of noble metal nanocrystals used in heterogeneous organic transformations has remained a significant challenge, hindering their use in industry. Herein, highly catalytic Pd nanoparticles (NPs) were first prepared having a yield of >98% by a novel hydrothermal method using PVP as the reducing cum stabilizing agent that exhibited excellent turnover frequencies of â¼38,000 h-1 for Suzuki-Miyaura cross-coupling and â¼1200 h-1 for catalytic reduction of nitroarene compounds in a benign aqueous reaction medium. The Pd NPs were more efficient for cross-coupling of aryl compounds with electron-donating substituents than with electron-donating ones. Further, to improve their recyclability, a strategy was developed to embed these Pd NPs on mechanically robust polyurethane foam (PUF) for the first time and a "dip-catalyst" (Pd-PUF) containing 3D interconnected 100-500 µm pores was constructed. The PUF was chosen as the support with an expectation to reduce the fabrication cost of the "dip-catalyst" as the production of PUF is already commercialized. Pd-PUF could be easily separated from the reaction aliquot and reused without any loss of activity because the leaching of Pd NPs was found to be negligible in the various reaction mixtures. We show that the Pd-PUF could be reused for over 50 catalytic cycles maintaining a similar activity. We further demonstrate a scale-up reaction with a single-reaction 1.5 g yield for the Suzuki-Miyaura cross-coupling reaction.
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In view of a limited rationale available for designing metal nanocrystals (NCs) to achieve high catalytic activities across various chemical transformations, we offer a new perspective on the optimization of the 'solvent-of-nanocrystal-synthesis' that, to an extent, would help bypass the tedious characterization needs. A systematic improvement in a catalyst is hindered because (i) it relies on size & shape control protocols, surface characterization, understanding molecular transformation mechanisms, and the energetics of the reactant-catalyst interactions, requiring the involvement of different domains experts, and (ii) the insights developed using model reactions may not easily extend to other reactions, although the current studies count on such a hypothesis. In support of (ii), by taking Pd NCs as catalysts and two distinct reaction types, viz. Suzuki coupling and nitroarene reduction, we show to what great extent the reaction rates may vary even for the seemingly similar reactions by using the same NCs. More importantly, for challenge (i), we demonstrate how the addition of a single-step to the current protocol of 'catalyst-synthesis and activity test' can potentially lead to the development of highly active catalysts by first finding a suitable solvent for the NC synthesis, while such solvent-effects are barely considered unlike the same in organic transformation reactions as a matter of routine, for example.
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Mushrooms are rich in ergosterol, a precursor of ergocalciferol, which is a type of vitamin D2. The conversion of ergosterol to ergocalciferol takes place in the presence of UV radiation by the cleavage of the "B-ring" in the ergosterol. As the UV radiation cannot penetrate deep into the tissue, only minimal increase occurs in sunlight. In this study, upconversion nanoparticles with the property to convert deep-penetrating near-infrared radiation to UV radiation have been cast into a disk to use sunlight and emit UV radiation for vitamin D conversion. An engineered upconversion nanoparticle (UCNP) disk with maximum particles and limited clusters demonstrates â¼2.5 times enhanced vitamin D2 conversion.
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Luz Solar , Rayos Ultravioleta , Ergosterol , Rayos Ultravioleta/efectos adversos , Vitamina D , VitaminasRESUMEN
Selective oxidation of amines to imines using sunlight as clean and renewable energy source is an important but challenging chemical transformation because of high reactivity of the generated imines and lack of visible light-responsive materials with high conversion rates. In addition, oxygen gas has to be purged in the reaction mixture in order to increase the reaction efficiency which, in itself, is an energy-consuming process. Herein, we report, for the first time, the use of Ag3PO4 as an excellent photocatalyst for the oxidative coupling of benzyl amines induced by ambient air in the absence of any external source of molecular oxygen at room temperature. The conversion efficiency for the selective oxidation of benzyl amine was found to be greater than 95% with a selectivity of >99% after 40 min of light irradiation indicating an exceptionally high conversion efficiency with a rate constant of 0.002 min-1, a turnover frequency of 57 h-1, and a quantum yield of 19%, considering all of the absorbed photons. Ag3PO4, however, is known for its poor photostability owing to a positive conduction band position and a favorable reduction potential to metallic silver. Therefore, we further employed a simple catalyst regeneration strategy and showed that the catalyst can be recycled with negligible loss of activity and selectivity.
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Solar-driven photocatalysis is emerging as a key chemical transformation strategy due to its favourable energy economy. However, in photocatalytic oxidation reactions where molecular oxygen (O2) is a reactant, achieving higher efficiency requires an O2-saturated environment in order to maintain a high oxygen level on the catalyst surface, necessitating an additional energy-consuming step of O2 separation from air. Here we show that in the presence of carbon quantum dots (CQDs), the oxygen content and the ability of O2 to diffuse in water increase significantly. We first demonstrate a novel strategy to convert several grams of polyethylene, a stubborn pollutant, into highly photoactive CQDs by stepwise dehydrogenation and graphitization. In a typical CQD concentration of â¼1 mg ml-1, the oxygen level in water reaches â¼640 µM, double that of pure water inferring an extremely high O2 content of â¼1 wt% associated with CQDs under ambient conditions. Therefore, when the CQDs were used to catalyze photo-oxidation of aromatic alcohols by sunlight, the efficiency was found higher than previous instances despite those employing high oxygen pressure, temperature and expensive materials. Besides waste polyethylene utilization, the uniqueness of oxygen enrichment in CQD solutions may offer immense prospects including those in photo-oxidation reactions.
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Herein, we show that composites of Bi3TaO7-Bi4TaO8X (X = Cl, Br), two important Bi- and Ta-based light-responsive phases, can be prepared by high temperature, ambient air treatment of the precursors including easily oxidizable BiOX that retain the halide phases in excess of 60% and exhibit high photocatalytic activity. Furthermore, when these phases were loaded with less than 1% noble metals (Pd, Pt, Ag), nearly complete separation of the photogenerated excitons was observed, leading to a significant enhancement in the photocatalytic activity.