Bottom-up Synthesis Approach Research Articles

Pore engineering of Porous Materials: Effects and Applications.

Porous materials, characterized by their controllable pore size, high specific surface area, and controlled space functionality, have become cross-scale structures with microenvironment effects and multiple functions and have gained tremendous attention in the fields of catalysis, energy storage, and biomedicine. They have evolved from initial nanopores to multiscale pore-cavity designs with yolk-shell, multishells, or asymmetric structures, such as bottle-shaped, multichambered, and branching architectures. Various synthesis strategies have been developed for the interfacial engineering of porous structures, including bottom-up approaches by using liquid-liquid or liquid-solid interfaces "templating" and top-down approaches toward chemical tailoring of polymers with different cross-linking degrees, as well as interface transformation using the Oswald ripening, Kirkendall effect, or atomic diffusion and rearrangement methods. These techniques permit the design of functional porous materials with diverse microenvironment effects, such as the pore size effect, pore enrichment effect, pore isolation and synergistic effect, and pore local field enhancement effect, for enhanced applications. In this review, we delve into the bottom-up and top-down interfacial-oriented synthesis approaches of porous structures with advanced structures and microenvironment effects. We also discuss the recent progress in the applications of these collaborative effects and structure-activity relationships in the areas of catalysis, energy storage, electrochemical conversion, and biomedicine. Finally, we outline the persisting obstacles and prospective avenues in terms of controlled synthesis and functionalization of porous engineering. The perspectives proposed in this paper may contribute to promote wider applications in various interdisciplinary fields within the confined dimensions of porous structures.

(Invited) 3D Carbon-Based Hierarchical Electrodes for Energy Storage

: Carbon-based 3D hierarchical electrodes with appropriate spatial distributions of pores are expected to empower rapid and controllable electrochemical reactions. The ability to fabricate such an electrode, with tunable geometries comprised of continuous nano- and micro-conduits, allows simultaneous optimization of conversion capacity as well as reaction rate. Such manufacturability holds great potential to redefine the future of energy storage, electrocatalysis and chemical production for a sustainable future.In this presentation, I will outline two convergent strategies that involve the integration of additive manufacturing with several decades of advancements in nanomaterials synthesis, coupled with conventional pyrolysis – for creating such electrodes. The primary structure of 3D carbon-based electrodes was fabricated by either direct 3D writing, or the transition metal assisted pyrolysis of 3D-printed polymer templates. The secondary structure was established by employing bottom-up synthesis approaches: (a) SiO2 nanoparticle templates to create nanoscopic porous structures or (b) nanochannels formed through direct growth of carbon nanotubes. We have demonstrated that the primary and secondary structures can be formed by a single step. After monolithic integration of a tertiary structure to reveal sites for electrochemical conversion, these 3D architected electrodes offer impressive charge storage capacities while maintain excellent rate capability.By exploiting the short mass diffusion lengths, we have demonstrated that the new energy storage devices can operate at temperatures as low as -70°C without the requirement of a heater. Furthermore, the incorporation of a high loading of active materials in our 3D electrodes allows for concurrent enhancement of both energy density and power density. These scalable fabrication protocols address two critical challenges – sluggish mass transfer in 3D and the lack of accessible active sites, thereby offering a pathway to harness electrochemical reactions in 3D. This work offers an adaptable solution across a broad spectrum of industries.

Electrochemical Knocking-Down of Zn Metal Clusters into Single Atoms.

Single Atoms Catalysts (SACs) have emerged as a class of highly promising heterogeneous catalysts, where the traditional bottom-up synthesis approaches often encounter considerable challenges in relation to aggregation issues and poor stability. Consequently, achieving densely dispersed atomic species in a reliable and efficient manner remains a key focus in the field. Herein, we report a new facile electrochemical knock-down strategy for the formation of SACs, whereby the metal Zn clusters are transformed into single atoms. While a defect-rich substrate plays a pivotal role in capturing and stabilizing isolated Zn atoms, the feasibility of this novel strategy is demonstrated through a comprehensive investigation, combining experimental and theoretical studies. Furthermore, when studied in exploring for potential applications, the material prepared shows a remarkable improvement of 58.21% for the Li+ storage and delivers a capacity over 300 Wh kg-1 after 500 cycles upon the transformation of Zn clusters into single atoms.

Ion Transport Behavior in van der Waals Gaps of 2D Materials.

2D materials, with advantages of atomic thickness and novel physical/chemical characteristics, have emerged as the vital building blocks for advanced lamellar membranes which possess promising potential in energy storage, ion separation, and catalysis. When 2D materials are stacked together, the van der Waals (vdW) force generated between adjacent layered nanosheets induces the construction of an ordered lamellar membrane. By regulating the interlayer spacing down to the nanometer or even sub-nanometer scale, rapid and selective ion transport can be achieved through such vdW gaps. The further improvement and application of qualified 2D materials-based lamellar membranes (2DLMs) can be fulfilled by the rational design of nanochannels and the intelligent micro-environment regulation under different stimuli. Focusing on the newly emerging advances of 2DLMs, in this review, the common top-down and bottom-up synthesis approaches of 2D nanosheets and the design strategy of functional 2DLMs are briefly introduced. Two essential ion transport mechanisms within vdW gaps are also involved. Subsequently, the responsive 2DLMs based on different types of external stimuli and their unique applications in nanofluid transport, membrane-based filters, and energy storage are presented. Based on the above analysis, the existing challenges and future developing prospects of 2DLMs are further proposed.

ADOR zeolite with 12 × 8 × 8-ring pores derived from IWR germanosilicate.

Zeolites have been well known for decades as catalytic materials and adsorbents and are traditionally prepared using the bottom-up synthesis method. Although it was productive for more than 250 zeolite frameworks, the conventional solvothermal synthesis approach provided limited control over the structural characteristics of the formed materials. In turn, the discovery and development of the Assembly-Disassembly-Organization-Reassembly (ADOR) strategy for the regioselective manipulation of germanosilicates enabled the synthesis of previously unattainable zeolites with predefined structures. To date, the family tree of ADOR materials has included the topological branches of UTL, UOV, IWW, *CTH, and IWV zeolites. Herein, we report on the expansion of ADOR zeolites with a new branch related to the IWR topology, which is yet unattainable experimentally but theoretically predicted as highly promising adsorbents for CO2 separation applications. The optimization of not only the chemical composition but also the dimensions of the crystalline domain in the parent IWR zeolite in the Assembly step was found to be the key to the success of its ADOR transformation into previously unknown IPC-17 zeolite with an intersecting 12 × 8 × 8-ring pore system. The structure of the as-prepared IPC-17 zeolite was verified by a combination of microscopic and diffraction techniques, while the results on the epichlorohydrin ring-opening with alcohols of variable sizes proved the molecular sieving ability of IPC-17 with potential application in heterogeneous catalysis. The proposed synthesis strategy may facilitate the discovery of zeolite materials that are difficult or yet impossible to achieve using a traditional bottom-up synthesis approach.

Regulation of the multi-emission centers in carbon dots via a bottom-up synthesis approach

Understanding the luminescence mechanisms and regulating the emission centers of carbon dots (CDs) are important for advancing their related applications. In this work, we systematically investigate the formation processes of multi-emission centers in CDs synthesized through a bottom-up approach by controlling the solvothermal reaction temperature. CDs synthesized at a lower temperature (140 °C, 140-CDs) exhibit smaller particle sizes (3–4 nm) with dominant green–yellow emission, while CDs synthesized at a higher temperature (180 °C, 180-CDs) exhibit larger particle sizes (8–9 nm) with enhanced red emission and emerging near-infrared (NIR) emission. The green–yellow emission and red emission originate from the core state and the surface-related state, respectively, and the emissions could be regulated by temperature-controlled dehydration and carbonization processes. The clear NIR emission center in 180-CDs is attributable to the increased content of radical defects in the cores during the increased dehydration and carbonization processes during higher-temperature solvothermal treatment.

Fabrication of single Co sites in graphitic carbon nitride via the ion exchange to boost aerobic cyclohexane oxidation

Cyclohexane oxidation is an industrial process for manufacturing cyclohexanol, cyclohexanone and adipic acid, while it remains a huge challenge to develop highly efficient catalysts for intensifying this process. Herein, a bottom-up synthesis approach, coupling the one-pot and ion exchange strategy, is developed to fabricate atomically dispersed Co on graphitic carbon nitride (g-C3N4) for the aerobic cyclohexane oxidation. The loading of the single-atom Co on Co/g-C3N4 can be facilely tuned by adjusting the ion exchange extent of Na + on Na/g-C3N4 precursor. Comprehensive characterizations demonstrate the atomical location of Co in sixfold cavities of g-C3N4, accompanied by the electron interaction between Co atoms and g-C3N4. The resulting Co/g–C3N4–1 catalyst possesses the superior oxidation performance with the 28.8 % cyclohexane conversion and 93.0 % overall selectivity toward desired products, and it also exhibits an acceptable universality to the catalytic oxidation of various hydrocarbons. The mechanism study revealed that besides the dissociation of O2 molecules on single-atom Co sites, the electron-rich g-C3N4 surface stemming from atomic Co doping facilitated the cyclohexane adsorption, which synergically boosted the subsequent oxidation reaction following the surface catalytic mechanism. We anticipate that such a concept of fabricating atomically dispersed metals via the ion exchange strategy provides a novel insight and feasible approach for the design of highly efficient single-atom catalysts for the cyclohexane oxidation and beyond.

On-Surface Synthesis of Graphene Nanoribbons with Atomically Precise Structural Heterogeneities and On-Site Characterizations.

Graphene nanoribbons (GNRs) are strips of graphene, with widths of a few nanometers, that are promising candidates for future applications in nanodevices and quantum information processing due to their highly tunable structure-dependent electronic, spintronic, topological, and optical properties. Implantation of periodic structural heterogeneities, such as heteroatoms, nanopores, and non-hexagonal rings, has become a powerful manner for tailoring the designer properties of GNRs. The bottom-up synthesis approach, by combining on-surface chemical reactions based on rationally designed molecular precursors and in situ tip-based microscopic and spectroscopic techniques, promotes the construction of atomically precise GNRs with periodic structural modulations. However, there are still obstacles and challenges lying on the way toward the understanding of the intrinsic structure-property relations, such as the strong screening and Fermi level pinning effect of the normally used transition metal substrates and the lack of collective tip-based techniques that can cover multi-internal degrees of freedom of the GNRs. In this Perspective, we briefly review the recent progress in the on-surface synthesis of GNRs with diverse structural heterogeneities and highlight the structure-property relations as characterized by the noncontact atomic force microscopy and scanning tunneling microscopy/spectroscopy. We furthermore motivate to deliver the need for developing strategies to achieve quasi-freestanding GNRs and for exploiting multifunctional tip-based techniques to collectively probe the intrinsic properties.

Recent Progress in Azobenzene-Based Supramolecular Materials and Applications.

Azobenzene-containing small molecules and polymers are functional photoswitchable molecules to form supramolecular nanomaterials for various applications. Recently, supramolecular nanomaterials have received enormous attention in material science because of their simple bottom-up synthesis approach, understandable mechanisms and structural features, and batch-to-batch reproducibility. Azobenzene is a light-responsive functional moiety in the molecular design of small molecules and polymers and is used to switch the photophysical properties of supramolecular nanomaterials. Herein, we review the latest literature on supramolecular nano- and micro-materials formed from azobenzene-containing small molecules and polymers through the combinatorial effect of weak molecular interactions. Different classes including complex coacervates, host-guest systems, co-assembled, and self-assembled supramolecular materials, where azobenzene is an essential moiety in small molecules, and photophysical properties are discussed. Afterward, azobenzene-containing polymers-based supramolecular photoresponsive materials formed through the host-guest approach, polymerization-induced self-assembly, and post-polymerization assembly techniques are highlighted. In addition to this, the applications of photoswitchable supramolecular materials in pH sensing, and CO2 capture are presented. In the end, the conclusion and future perspective of azobenzene-based supramolecular materials for molecular assembly design, and applications are given.

Large-Area Synthesis of Ferromagnetic Fe5- x GeTe2 /Graphene van der Waals Heterostructures with Curie Temperature above Room Temperature.

Van der Waals (vdW) heterostructures combining layered ferromagnets and other 2D crystals are promising building blocks for the realization of ultracompact devices with integrated magnetic, electronic, and optical functionalities. Their implementation in various technologies depends strongly on the development of a bottom-up scalable synthesis approach allowing for realizing highly uniform heterostructures with well-defined interfaces between different 2D-layered materials. It is also required that each material component of the heterostructure remains functional, which ideally includes ferromagnetic order above room temperature for 2D ferromagnets. Here, it is demonstrated that the large-area growth of Fe5- x GeTe2 /graphene heterostructures is achieved by vdW epitaxy of Fe5- x GeTe2 on epitaxial graphene. Structural characterization confirms the realization of a continuous vdW heterostructure film with a sharp interface between Fe5- x GeTe2 and graphene. Magnetic and transport studies reveal that the ferromagnetic order persists well above 300 K with a perpendicular magnetic anisotropy. In addition, epitaxial graphene on SiC(0001) continues to exhibit a high electronic quality. These results represent an important advance beyond nonscalable flake exfoliation and stacking methods, thus marking a crucial step toward the implementation of ferromagnetic 2D materials in practical applications.

Hollow multishelled structured graphdiyne realized radioactive water safe-discharging

High toxicity, and long-term retention of heavy metallic ions in surface water environment pose threats to the stability of ecosystems and vitality of creatures including human beings. The well-adopted approach always facing the challenge of sustainability and energy consumption. Moreover, discharging standard is rather strict for radioactive metallic element containing water, which makes finding an appropriate and effective way for ion-removing urgent. Particularly, among various treatment approaches to remove metal ions from water, solar-driven steam generation is considered as an eco-friendly and sustainable strategy, but the removing of radioactive ions is rarely considered. In this paper, with the bottom-up synthesis approach, we fabricated the 3D graphdiyne (GDY) with hollow multishelled structure (HoMS) for the first time. Because of the advantages of HoMS, a stable evaporation rate of 2.7 kg m−2 h−1 has been achieved by GDY-HoMS. Notably, owning to the interaction between sp-C of GDY and the empty orbit of metallic atoms, the heavy metallic elements were intercepted in the GDY film, resulting an ultra-efficient ion removing ability. Especially, the ion concentration was decreased by six to seven orders magnitude for Sr2+ and Cs+-contained radioactive water after treatment, reaching the national radioactive water discharge standard, while the ion concentration for U(VI) has been decreased to meet the drinkable water standard.

Evaluation of Mesoporous TiO2 Layers as Glucose Optical Sensors.

Porous materials are currently the basis of many optical sensors because of their ability to provide a higher interaction between the light and the analyte, directly within the optical structure. In this study, mesoporous TiO2 layers were fabricated using a bottom-up synthesis approach in order to develop optical sensing structures. In comparison with more typical top-down fabrication strategies where the bulk constitutive material is etched in order to obtain the required porous medium, the use of a bottom-up fabrication approach potentially allows increasing the interconnectivity of the pore network, hence improving the surface and depth homogeneity of the fabricated layer and reducing production costs by synthesizing the layers on a larger scale. The sensing performance of the fabricated mesoporous TiO2 layers was assessed by means of the measurement of several glucose dilutions in water, estimating a limit of detection even below 0.15 mg/mL (15 mg/dL). All of these advantages make this platform a very promising candidate for the development of low-cost and high-performance optical sensors.

Bottom-Up Synthesis Strategies Enabling the Investigation of Metal Catalyst-Carbon Support Interactions

The structural versatility and vibrant surface chemistry of carbon materials offer tremendous opportunities for tailoring the catalytic performance of supported metal nanoparticles through the modulation of interfacial metal-support interactions (MSI). MSI’s geometric and structural effects are well documented for these materials. However, other potential support effects such as electronic metal-carbon interactions remain poorly understood. Such limitations are tied to constraints intrinsic to commonly available carbon materials such as activated carbon (e.g., microporosity) and the top-down approach that is often used for their synthesis. Nonetheless, it is crucial to understand the interplay between the structure, properties, and performance of carbon-supported metal catalysts to take steps toward rationalizing their design. The present study investigates promising and scalable bottom-up synthesis approaches, namely hydrothermal carbonization (HTC) and evaporation-induced self-assembly (EISA), that offer great flexibility for controlling the carbon structure. The opportunities and limitations of the methods are discussed with a particular focus on harnessing the power of oxygen functionalities. A remarkable production yield of 32.8% was achieved for mesoporous carbons synthesized via EISA. Moreover, these carbon materials present similar external surface areas of 316 ± 19 m2/g and average pore sizes of 10.0 ± 0.1 nm while offering flexibility to control the oxygen concentration in the range of 5–26 wt%. This study provides the cornerstone for future investigations of metal-carbon support interactions and the rational design of these catalysts.

Silk nanofibril as nanobinder for preparing COF nanosheet-based proton exchange membrane

Two-dimensional covalent organic framework nanosheets (CONs) with ultrathin thickness and porous crystalline nature show substantial potential as novel membrane materials. However, bringing CONs materials into flexible membrane form is a monumental challenge due to the limitation of weak interactions among CONs. Herein, one-dimensional silk nanofibrils (SNFs) from silkworm cocoon are designed as the nanobinder to link sulfonated CON (SCON) into robust SCON-based membrane through vacuum-filtration method. Ultrathin and large lateral-sized SCONs are synthesized via bottom-up interface-confined synthesis approach. Benefiting from high length-diameter ratio of SNF and rich functional groups in both SNF and SCON, two-dimensional (2D) SCONs are effectively connected together by physical entanglement and strong H-bond interactions. The resultant SCON/SNF membrane displays dense structure, high mechanical integrity and good stability. Importantly, the rigid porous nanochannels of SCON, high-concentration –SO3H groups insides the pores and H-bonds at SCON–SNF interfaces impart SCON/SNF membrane high-rate proton transfer pathways. Consequently, a superior proton conductivity of 365 mS cm−1 is achieved at 80 °C and 100% RH by SCON/SNF membrane. This work offers a promising approach for connecting 2D CON materials into flexible membrane as high-performance solid electrolyte for hydrogen fuel cell and may be applied in membrane-related other fields.

Preparation of two-dimensional pyrazine-linked conjugated organic skeletons and their paramagnetic properties

<p indent=0mm>A two-dimensional pyrazine-linked conjugated organic framework with good crystallinity, namely HATP–HKH powder, was successfully prepared by a bottom-up synthesis approach. The structure and magnetic property of the material were characterized by powder X-ray diffraction patterns, Fourier-transform infrared spectra, high-resolution transmission microscopy, atomic force microscopy, superconducting quantum interferometer device magnetometer, electron spin resonance spectroscopy, and other instruments. The HATP–HKH nanosheets prepared by the liquid-phase exfoliation showed a height in the range of <sc>0.8−1.4 nm.</sc> The structure of the nanosheets was analogous to that of graphene-antidot lattices. At <sc>2 K,</sc> the material exhibited a typical paramagnetic behavior with the magnetization of 0.029 emu g⁻¹. Such a material could be developed and applied in the electronics and spintronic devices.

Sustainable transformation of natural silica-rich solid and waste to hierarchical zeolites for sugar conversion to hydroxymethylfurfural (HMF)

The expansive development of using waste materials to synthesize multifaceted functional materials is imperatively important in both economic and environmental aspects. Herein, natural silica-rich solids and wastes, including sand and scrap glass were successfully transformed to high value-added nano-aluminosilicates with the particle size under 40 nm, using a simple sol-gel method in the absence of dispersing agent. To demonstrate the further utilization of this material, a bottom-up synthesis approach has been simply implemented to fabricate the well-defined micro-mesoporous ZSM-5 with low Si/Al ratio using the prepared nano-aluminosilicates derived from natural silica-rich solids and wastes as both silica and alumina raw materials. The zeolite synthesis was systematically investigated as a function of water content in the synthesis gel and hydrothermal synthesis time. It is distinctly elucidated that the water content and hydrothermal synthesis time strongly effect the formation of hierarchical ZSM-5. Intriguingly, the integrating benefits between high acidity of aluminum-rich ZSM-5 and combined micro-mesoporous zeolite features can highly enhance the catalytic performances of fructose dehydration to hydroxymethylfurfural (HMF) with almost 80% yield. This contribution demonstrates the scientific opportunities to utilize waste materials to multifaceted functional materials as well as its application for sugar transformation to high value-added platform chemicals in biorefinery application. • Nano-aluminosilicates have been successfully synthesized using natural silica-rich solid and waste materials. • Aluminum-rich hierarchical ZSM-5 has been fabricated using the obtained nano-aluminosilicates. • Outstanding high acidity and specific surface area of aluminum-rich hierarchical ZSM-5 can be observed. • The aluminum-rich hierarchical H-ZSM-5 demonstrates the promising catalytic activity toward sugar to HMF.

Combined Bottom-Up and Top-Down Approach for Highly Ordered One-Dimensional Composite Nanostructures for Spin Insulatronics.

Engineering magnetic proximity effects-based devices requires developing efficient magnetic insulators. In particular, insulators, where magnetic phases show dramatic changes in texture on the nanometric level, could allow us to tune the proximity-induced exchange splitting at such distances. In this paper, we report the fabrication and characterization of highly ordered two-dimensional arrays of LaFeO3 (LFO)–CoFe2O4 (CFO) biphasic magnetic nanowires, grown on silicon substrates using a unique combination of bottom-up and top-down synthesis approaches. The regularity of the patterns was confirmed using atomic force microscopy and scanning electron microscopy techniques, whereas magnetic force microscopy images established the magnetic homogeneity of the patterned nanowires and absence of any magnetic debris between the wires. Transmission electron microscopy shows a close spatial correlation between the LFO and CFO phases, indicating strong grain-to-grain interfacial coupling, intrinsically different from the usual core–shell structures. Magnetic hysteresis loops reveal the ferrimagnetic nature of the composites up to room temperature and the presence of a strong magnetic coupling between the two phases, and electrical transport measurements demonstrate the strong insulating behavior of the LFO–CFO composite, which is found to be governed by Mott-variable range hopping conduction mechanisms. A shift in the Raman modes in the composite sample compared to those of pure CFO suggests the existence of strain-mediated elastic coupling between the two phases in the composite sample. Our work offers ordered composite nanowires with strong interfacial coupling between the two phases that can be directly integrated for developing multiphase spin insulatronic devices and emergent magnetic interfaces.

Atomically Precise Dinuclear Site Active toward Electrocatalytic CO2 Reduction.

The development of atomically precise dinuclear heterogeneous catalysts is promising to achieve efficient catalytic performance and is also helpful to the atomic-level understanding on the synergy mechanism under reaction conditions. Here, we report a Ni2(dppm)2Cl3 dinuclear-cluster-derived strategy to a uniform atomically precise Ni2 site, consisting of two Ni1-N4 moieties shared with two nitrogen atoms, anchored on a N-doped carbon. By using operando synchrotron X-ray absorption spectroscopy, we identify the dynamically catalytic dinuclear Ni2 structure under electrochemical CO2 reduction reaction, revealing an oxygen-bridge adsorption on the Ni2-N6 site to form an O-Ni2-N6 structure with enhanced Ni-Ni interaction. Theoretical simulations demonstrate that the key O-Ni2-N6 structure can significantly lower the energy barrier for CO2 activation. As a result, the dinuclear Ni2 catalyst exhibits >94% Faradaic efficiency for efficient carbon monoxide production. This work provides bottom-up target synthesis approaches and evidences the identity of dinuclear sites active toward catalytic reactions.

Oscillatory Electrodeposition of Cu/Cu2o: A Study on the Influence of Ligands in Cu(II) Complexes

Self-organization is a powerful tool for the synthesis of new materials, among a wide variety of processes that exhibit this phenomenon, electrochemical ones are promising candidates in which the main contributions can be divided between electrodeposition and electrodissolution systems.1 Potential and/or current oscillations have already been observed in several electrodeposition reactions and culminated in the formation of different structures under micro and nanoscale such as multilayers, spiral waves and dendrites.Periodic potential oscillations related to alternate electrodeposition of Cu and Cu/Cu2O, recorded in the form multilayered architecture were first reported by Switzer and collaborators,2 and further explored in the presence of other ligands such as tartrate and citrate.The oscillations that occur under galvanostatic regime are detected in a broad range of pH and current densities values, that directly affect the period and amplitude of the oscillations. Therefore, as the material morphology and properties are directed related to the dynamical behavior of the system, it is of major importance to understand deeply the role of the experimental variables on the system. Although direct relationships between experimental parameters, especially at short range studies, are consistently reported at the literature, multivariate statistical analysis revealed a more complex dependence on the frequency including quadratic terms.3 Concerning the chemical influence of the ligand over the oscillatory electrodeposition of Cu/Cu2O, we have investigated the effect of lactate (Figs. A and C) and tartrate (Figs. B and D) ligands in the oscillation period (Figs. A and B) and amplitude (Figs. C and D).4 The potential oscillations at the Cu(II)-lactate and Cu(II)-tartrate systems are detected in different ranges of pH and current densities values for each system, that affect the period and amplitude of the oscillations as portrayed at the diagrams in Figs. A to D. Although a strict parallel of the systems can not be performed, the main characteristics are the period and amplitude variation when the lactate is replaced by tartrate in the reaction media. On balance, the potential oscillations in the Cu(II)−tartrate system exhibit larger periods and lower amplitude values in relation to the Cu(II)−lactate one. Beyond that, there is a significant suppression of the oscillation domain in the tartrate system, that can be connected to an apparent inhibition effect, as a result of the stronger adsorption of tartrate anions and/or its metallic complexes. In fact, the presence of a poisoning species on the surface, that acts as spectator of the reaction, can induce the increase of the oscillation period and suppress the Hopf domain, as previously reported.The oscillation mechanism introduced by Switzer et al., further detailed by Leopold et al. and updated by our group, taking into account recent available structural information (Figs. E and F), describes the alternated deposition of copper and copper oxide, and considers pH interfacial variation as being an essential step for the oscillation mechanism. Supposing that only a buffering effect can alter the oscillation period, as stated before by previous investigations, the buffering capacity found in the lactate complex (Fig. E) should be less effective when compared to the tartrate one (Fig. F). This can be explained from the ligand structures: the second carbonyl and hydroxy groups available for protonation/deprotonation (tartrate vs. lactate complex) lead to an increase in the buffering capacity, besides the concentration of these species in solution. Since the oscillating period is reduced when the solution pH is increased, a longer period observed for the tartrate complex means that this system possesses a higher buffering capacity compared to that for the lactate complex.Even though of significant importance, this mechanism does not account for the anion adsorption and/or the respective complexes dissolved in the electrolyte and as observed experimentally, which is an important consideration to be made in the description of the oscillatory electrodeposition. The surface blocking and buffering effect are enhanced when tartrate molecules are utilized as the ligand (in comparison with lactate system), and both mechanisms seem to control the dynamic properties of the electrochemical oscillator simultaneously. Therefore, we show that chemical structures or functions of the reactants could be altered to induce an autonomous growth of a target material, giving rise to a bottom-up synthesis approach. This is of great value especially since Cu and Cu2O interfaces are employed in many fields, such as electrocatalysis in the CO2 electroreduction.[1] M. R. Pinto, et al. ChemElectroChem 2020. [2] J. A. Switzer, et al. Adv. Mater. 1997.[3] B. T. Kitagaki, et al. Phys. Chem. Chem. Phys. 2019.[4] M. R. Pinto, ei al. J. Phys. Chem. C 2020. Figure 1

Insight into the Molecular Model in Carbon Dots through Experimental and Theoretical Analysis of Citrazinic Acid in Aqueous Solution

The molecular emission model is the most accredited one to explain the emission properties of carbon dots (CDs) in a low-temperature bottom-up synthesis approach. In the case of citric acid and urea, the formation of a citrazinic acid (CZA) single monomer and oligomers is expected to affect the optical properties of the CDs. It is therefore mandatory to elucidate the possible role of weak bonding interactions in determining the UV absorption spectrum of some molecular aggregates of CZA. Although this carboxylic acid is largely exploited in the synthesis of luminescent CDs, a full understanding of its role in determining the final emission spectra of the produced CDs is still very far to be achieved. To this aim, by relying on purely first-principles density functional theory calculations combined with experimental optical characterization, we built and checked the stability of some molecular aggregates, which could possibly arise from the formation of oligomers of CZA, mainly dimers, trimers, and some selected tetramers. The computed vibrational fingerprint of the formation of aggregates is confirmed by surface-enhanced Raman spectroscopy. The comparison of experimental data with calculated UV absorption spectra showed a clear impact of the final morphology of the aggregates on the position of the main peaks in the UV spectra, with particular regard to the 340 nm peak associated with n-π* transition.