Post-synthesis Process Research Articles

Direct Synthesis of Perovskite Quantum Dot Photoresist for Direct Photolithography.

Perovskite quantum dots (PQDs) photoresists are promising building blocks for photolithographically patterned devices. However, their complex synthesis and combination processes limit their optical properties and potential patterning applications. Here, we present an exceptionally simple strategy for the synthesis of PQDs photoresist. Unlike traditional approaches that involve centrifugation, separation, and combination processes, our direct synthesis technique using polymerizable acrylic monomer as solvent to fabricate PQDs photoresists without complex post-synthesis process. We demonstrate that the change in solubility of the precursors is the main reason for the formation of PQDs in the polymerizable monomer. By direct photolithography, colorful PQD patterns with high photoluminescence quantum yields and excellent fluorescence uniformity are successfully demonstrated. This work opens a new avenue for the direct synthesis of PQDs photoresist, expanding their applications in various integrated applications, such as photonic, energy harvesting, and optoelectronic devices.

(Invited) Single Crystal Ni-Rich Cathode Materials: Synthesis, Scaleup and Validation

Synthesis of high-performance single crystal Ni-rich NMC, especially when Ni≥0.8, poses a challenge. A conflict exists because as Ni content increase in NMC811, a lower calcination temperature is preferred due to Ni reduction at elevated temperatures, while high temperatures favour single crystal growth.Therefore, molten salt is sometimes employed as the reaction media to promote growth of single crystal NMC811. In general, four approaches for synthesizing of Ni-rich NMC single crystals: molten salt, hydrothermal, direct solid-state synthesis and multi-step lithiation. Molten salt and hydrothermal approaches result in the formation of well-segregated large crystals, but they also increase manufacturing cost. Direct solid-state synthesis, which involves ball milling all precursors together followed by calcination, is a time-saving approach. However, it poses challenge for impurity control due to contamination from milling media, and it can damage the material structure. The calcination of TM(OH)2 precursor with LiOH at very high sintering temperatures forms micron-sized primary particles which, however, still exhibit significantly agglomerated. A post-synthesis milling process is required to break down those NMC811 crystal clusters.This talk will discuss an innovative nanoscale phase separation approach for synthesis of high-performance single crystal NMC811 that is readily adaptable for industry manufacturing. The reaction mechanism of single crystal growth is investigated to understand the synthesis-morphology-performance relationship in growing single crystal NMC811 in the absence of molten salts. The scaled single crystal NMC811 is then further validated in a 2Ah Li-ion pouch cells, demonstrating 1000 stable cycling, confirming the feasibility of this new synthesis approach. This work provides new insights that are broadly applicable for cost-efficient large-scale synthesis of single crystals for different advanced battery technologies to accelerate deep decarbonization process.

Research progress of stationary phase of gas chromatography based on chiral organic frameworks

Enantiomers typically show different pharmacological, toxicological, and physiological properties. Thus, the preparation of enantiopure compounds is of great significance for human health and sustainable development. Compared with asymmetric catalysis, enantiomeric separation is simpler, faster, and more efficient; as such, it has become the preferred method for obtaining pure enantiomers. At present, enantiomeric separation methods mainly include chromatography, nanochannel membrane separation, selective adsorption, and recrystallization. In particular, gas chromatography (GC) plays an important role in enantioseparation because of its high sensitivity, excellent reproducibility, and outstanding processing capacity for various enantiomers. The stationary phase is key to the separation efficiency of GC, and more efficient, stable, and cost-effective materials that could serve as stationary phases are constantly being explored. Organic frameworks, such as covalent organic frameworks (COFs), metal-organic frameworks (MOFs), porous organic cages (POCs), metal-organic cages (MOCs), and hydrogen-bonded organic frameworks (HOFs), possess large specific surface areas, high porosities, tunable pore sizes, and easy functionalization, rendering them promising candidates for the separation of mixed analytes. Research has shown that the use of organic frameworks as stationary phases for GC results in excellent column efficiency and high resolution for various analytes, including n-alkanes, n-alcohols, polycyclic aromatic hydrocarbons, positional isomers, and organic fluorides. Furthermore, organic frameworks can be prepared as chiral stationary phases for GC by the intelligent introduction of a chiral moiety, thereby enabling the efficient separation of enantiomers. Synthetic strategies for chiral organic frameworks are primarily categorized as post-synthesis or bottom-up approaches. In general, the post-synthesis strategy can introduce various chiral sites to the framework; however, the distribution of chiral sites may not be uniform, and the ordered framework may be destroyed during the post-synthesis process. The bottom-up strategy allows for the uniform and precise distribution of chiral sites in the framework, but the synthesis of chiral monomers and the constraint between asymmetry and crystallinity limit its development. Chiral induction has been proposed as an alternative strategy for synthesizing chiral organic frameworks. The use of this strategy has led to the successful preparation of organic frameworks with abundant chiral sites and excellent crystallinity. Dynamic coating and in situ growth are the main approaches used to transform the as-prepared chiral organic frameworks into stationary phases. Notably, the in situ growth approach can yield chiral COF/MOF-coated capillary columns that provide high resolution for the separation of enantiomers with excellent repeatability and reproducibility. Nevertheless, owing to the slightly complex pretreatment process and the difficulty of synthesizing chiral organic frameworks, the in situ growth approach has not yet been widely applied. Owing to their excellent solvent processing performance, POCs, MOCs, and HOFs can be easily coated on the inner walls of columns to form membranes via dynamic or static coating. A series of enantiomers have been successfully separated and analyzed by immobilizing chiral COFs, MOFs, POCs, MOCs, and HOFs on GC capillary columns, demonstrating the great potential of chiral organic frameworks for enantiomeric separation. In general, the mechanisms by which chiral organic frameworks recognize enantiomers could be mainly categorized as van der Waals interactions, hydrogen bonding, π-π interactions, and size-exclusion effects. While molecular simulations can offer some insights into these recognition mechanisms, clarifying these mechanisms based on effective characterization remains challenging. In summary, organic frameworks show outstanding advantages for enantiomer separation. Given breakthroughs in synthetic strategies for chiral organic frameworks and the in-depth study of chiral recognition mechanisms, chiral organic frameworks may be expected to become an important aspect in the field of chiral materials, further realizing the large-scale analysis and production of chiral analytes. A total of 64 references, most of which are from the American Chemical Society, Springer Nature, Wiley Online Library, and Elsevier databases, are cited in this review.

Chemical transformation mechanism for blue-to-green emitting CsPbBr3 nanocrystals.

Recently, metal-halide perovskites have rapidly emerged as efficient light emitters with near-unity quantum yield and size-dependent optical and electronic properties, which have attracted considerable attention from researchers. However, the ultrafast nucleation rate of ionic perovskite counterparts severely limits the in-depth exploration of the growth mechanism of colloidal nanocrystals (NCs). Herein, we used an inorganic ligand nitrosonium tetrafluoroborate (NOBF4) to trigger a slow post-synthesis transformation process, converting non-luminescent Cs4PbBr6 NCs into bright green luminescent CsPbBr3 NCs to elucidate the concrete transformation mechanism via four stages: (i) the dissociation of pristine NCs, (ii) the formation of Pb-Br intermediates, (iii) low-dimensional nanoplatelets (NPLs) and (iv) cubic CsPbBr3 NCs, corresponding to the blue-to-green emission process. The desorption and reorganization of organic ligands induced by NO+ and the involvement of BF4- in the ligand exchange process played pivotal roles in this dissolution-recrystallization of NCs. Moreover, controlled shape evolution from anisotropic NPLs to NCs was investigated through variations in the amount of NOBF4. This further validates that additives exert a decisive role in the symmetry and growth of nanostructured perovskite crystals during phase transition based on the ligand-exchange mechanism. This finding serves as a source of inspiration for the synthesis of highly luminescent CsPbBr3 NCs, providing valuable insights into the chemical mechanism in post-synthesis transformation.

Regulating Charge Carrier Dynamics in Stable Perovskite Nanorods for Photo-Induced Atom Transfer Radical Polymerization.

Semiconducting nanocrystals have attracted world-wide research interest in artificial photosynthesis due to their appealing properties and enticing potentials in converting solar energy into valuable chemicals. Compared to 0D nanoparticles, 1D nanorods afford long-distance charge carriers separation and extended charge carriers lifetime due to the release of quantum confinement in axial direction. Herein, stable CsPbBr3 nanorods of distinctive dimensions are crafted without altering their properties and morphology via grafting hydrophobic polystyrene (PS) chains through a post-synthesis ligand exchange process. The resulting PS-capped CsPbBr3 nanorods exhibit a series of enhanced stabilities against UV irradiation, elevated temperature, and polar solvent, making them promising candidates for photo-induced atom transfer radical polymerization (ATRP). Tailoring the surface chemistry and dimension of the PS-capped CsPbBr3 nanorods endows stable, but variable reaction kinetics in the photo-induced ATRP of methyl methacrylate. The trapping-detrapping process of photogenerated charge carriers lead to extended lifetime of charge carriers in lengthened CsPbBr3 nanorods, contributing to a facilitated reaction kinetics of photo-induced ATRP. Therefore, by leveraging such stable PS-capped CsPbBr3 nanorods, the effects of surface chemistry and charge carriers dynamics on its photocatalytic performance are scrutinized, providing fundamental understandings for designing next-generation efficient nanostructured photocatalyst in artificial photosynthesis and solar energy conversion.

Fabrication and Characterization of Dielectric ZnCr2O4 Nanopowders and Thin Films for Parallel-Plate Capacitor Applications.

We report here the successful shape-controlled synthesis of dielectric spinel-type ZnCr2O4 nanoparticles by using a simple sol-gel auto-combustion method followed by successive heat treatment steps of the resulting powders at temperatures from 500 to 900 °C and from 5 to 11 h, in air. A systematic study of the dependence of the morphology of the nanoparticles on the annealing time and temperature was performed by using field effect scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD) and structure refinement by the Rietveld method, dynamic lattice analysis and broadband dielectric spectrometry, respectively. It was observed for the first time that when the aerobic post-synthesis heat treatment temperature increases progressively from 500 to 900 °C, the ZnCr2O4 nanoparticles: (i) increase in size from 10 to 350 nm and (ii) develop well-defined facets, changing their shape from shapeless to truncated octahedrons and eventually pseudo-octahedra. The samples were found to exhibit high dielectric constant values and low dielectric losses with the best dielectric performance characteristics displayed by the 350 nm pseudo-octahedral nanoparticles whose permittivity reaches a value of ε = 1500 and a dielectric loss tan δ = 5 × 10-4 at a frequency of 1 Hz. Nanoparticulate ZnCr2O4-based thin films with a thickness varying from 0.5 to 2 μm were fabricated by the drop-casting method and subsequently incorporated into planar capacitors whose dielectric performance was characterized. This study undoubtedly shows that the dielectric properties of nanostructured zinc chromite powders can be engineered by the rational control of their morphology upon the variation of the post-synthesis heat treatment process.

Effect of sintering temperature on microstructure, optical and dielectric properties in a low radio frequency range of a BaO:ZnO composite

Effect of sintering, between 550 and 950 °C, on dielectric properties of ceramic composite BaO:ZnO (BZO) was investigated in a low radio frequency range of 0.0–2.0 MHz. BZO ceramic composite was prepared by the facile autocombustion synthesis method. BaO and ZnO crystallized into tetragonal and hexagonal structures, respectively, coexist as an agglomerated microstructure inside the BZO composite. UV–Vis DRS, FTIR, photoluminescence and Raman spectroscopy were employed to find band gap energies, functionalization groups, excitation wavelength and the presence of vibrational modes of the sintered BZO composites. Scanning electron microscopy sufficed agglomerated structure of increasing particle size with temperature. Dielectric analysis showed that the maximum dielectric constant of 1.8 was observed for the composite sintered at 550 °C and then it decreased after heating at 650 °C. On further heating, an increase was observed in the dielectric constant of the BZO till 950 °C. The initial decrease was attributed to the presence of residual Ba(OH)2 phase. The loss tangent was reduced from 0.6 to 0.02 due to the post-synthesis sintering process. The sintered BZO exhibited increase in conductivity and decrease in resistivity in 0.0–2.0 MHz range. Similarly, the overall decline in real and imaginary permittivity was noticed with a uniform trend in the limit of 0.5–2.0 MHz. An increase in crystallite size from 41.36 to 92.54 nm for BaO and 22.23 to 40.99 nm for ZnO affected the dielectric constant. First, it decreased after heating at 650 °C and then increased up to 950 °C. During heating, a decrease in the interfacial polarization and an increase in the ionic polarization were attributed to the inter- and intra-crystallite boundary variations that played a role in the overall dielectric character of the BZO. The stability of dielectric parameters in the 0.25–2.0 MHz range suggested tuning these quantities by simply sintering process.

The role of aluminum in Sn-Al-beta zeolite catalyzing the conversion of glucose to methyl lactate

The preparation of H-Beta zeolites with different Si/Al ratios (Si/Al=14, Si/Al=288) was obtained by desiliconization and dealumination. Subsequently, Sn-Al-Beta catalysts were prepared by tin grafting and used for the conversion of glucose to methyl lactate. The results indicate that the yield of methyl lactate from the catalyst obtained using the parent H-beta synthesis with a high Si/Al ratio is higher than that of methyl lactate from the parent catalyst with a low initial Si/Al ratio. And the maximum methyl lactate yield of 46.66% was achieved on Sn-Al-Beta (DSi-277). In contrast, the yield of methyl lactate on Sn-Al-Beta (DAl-493) was 24.54%. Results from spectroscopic analysis and probe molecular FTIR indicated that the post-synthesis process altered the structure of the zeolite, which changed its aluminum concentration and existence form (1.8ppm chemical shift), Additionally, when the aluminum interacted with the Sn that had been added to the zeolite, it encouraged the Sn transformation to the high energy state and created the weaker Lewis acid site, as well as more effective action to improve reaction yield.

Top-down synthesis and enhancing device adaptability of graphene quantum dots

Quantum dots (QD) are rapidly making their way into several application sectors including optoelectronics, and there is a strong need to focus on non-toxic QDs. In this work, we have synthesized graphene QDs in the size range of 1.4–4.2 nm from inexpensive graphite by oxidative cleavage using a sulphuric and nitric acid mixture. A subsequent hydrogen peroxide oxidation step, investigated using two thermal budgets, has resulted in QDs with excellent photoluminescence (PL) intensity. Prolonged, higher temperature oxidation results in smaller size GQDs. X-ray photoelectron spectroscopy analysis confirmed the role of ·OH radicals in the oxidation process and Raman analysis revealed that the higher thermal budget oxidation results in lower defect density. To overcome the challenges in device adaptability due to the inherent acidity in the QDs, a post-synthesis neutralization process was devised. The neutralized GQDs were formed into a film to be used as the active layer in a photodetector device. Fluorescence decay analysis showed there is no significant change in lifetime because of the film formation process. The fabricated GQD photodetector device exhibited high photocurrent under ultraviolet illumination with an ON/OFF ratio of 400% at an applied bias of ±1 V. The device performance underlines the high potential for the non-toxic, top-down synthesized GQDs for application in optoelectronic devices.

Effect of Post-synthesis Processing on the Electrochemical Performance of Y2W3O12

Lithium-ion batteries (LIBs) are enabling the uptake of electric vehicles and providing grid-scale storage solutions for renewable energy generation. However, it is vital to develop new and advanced electrode materials for lithium-ion batteries to meet various applied considerations such as cost, safety, toxicity, and performance. Here, solid-state synthesized Y2W3O12 is demonstrated as a high-rate active anode material in lithium-ion batteries, producing an initial discharge capacity of 637 mAh/g although with a very poor initial Coulombic efficiency of 35%. To improve the performance, simple post-synthetic milling and carbon coating are investigated. Carbon coating of the material leads to significant performance enhancement in both the unmilled and milled samples. For instance, the unmilled carbon coated electrodes maintained a high capacity of ∼140 mAh/g at 1600 mA/g after 2000 cycles with no capacity fading from cycle 200 to 2000. Such a remarkable rate performance and an excellent long-term cycling stability showcase the great potential of this unconventional electrode material in fast-charge and high-power applications. This facile post-synthesis process can be easily applied to other electrode material candidates to enhance their electrochemical performance.

Impact of Post-Synthesis heat treatment avoidance on cobalt carbonate hydroxide as a Battery-Type electrode material

In this study, the electrochemical energy storage properties of one-dimensional (1D) hierarchical nanowire array (NWA) of cobalt carbonate hydroxide hydrate (Co6(CO3)2(OH)8·H2O) (CCH) is explored. The 1D nanostructure is advantageous due to their better charge/ion transport properties. The material was synthesized via. simple, and facile hydrothermal approach. The highlighting feature of this work lies in its post-synthesis process, where the authors deliberately avoided the post-synthesis heat treatment process to utilize the hydrated (x‧H2O) part associated with the lattice water which eventually led CCH in a unique robust crystal structure. Here, the authors have explored multifaceted aspects of 1D CCH NWAs, including the nanowire synthesis, their growth mechanism, and pseudocapacitive charge storage properties. The authors propose a novel charge storage mechanism, insertion pseudocapacitance, which depends on the (de)intercalation of cations (e.g., Li+, Na+, K+, and H+), where tunnels play a significant role in charge storage properties. In this type of charge-storage mechanism, cationic diffusion occur from the interior of the crystalline framework along with the surface-confined phenomena. The electrochemical energy storage performance in terms of specific capacity (Csp) is found to be 243.55 mAhg−1 @ 5 mVs−1 scan rate and 161.465 mAhg−1 at 2500 mAg−1 current density. The material exhibited excellent capacity retention of ∼ 95 % and ∼ 86 % at significantly higher current densities of 20,000 mAg−1 and 100,000 mAg−1, respectively. This work tries to establish the structure-electrochemical property correlation of the CCH which has an exceptional crystal structure that is deduced ∼ 20 years after its first report. Therefore, the authors emphasize exploring the fundamental understanding of the CCH from the crystallographic point of view and its relevance to electrochemical energy storage. This work will help in exploring the next-generation metal carbonate hydroxide hydrate-based (MCH) materials.

(Digital Presentation) Lithium Transition Metal Nitride Li7MnN4 (LMN) As Competitive Negative Electrode Material for Li-Ion Battery: Synthesis Optimization and High Energy Density of the NMC/Li5.3MnN4 Full Cell

Li-on battery (LIB) is an important technology which is widely used in portable electronic devices, electric vehicles (EV) and other energy storage applications. Commercial LIB has multiple choices as positive electrode materials such as layered transition metal oxides (LiCoO2, LiNi1-y-zMnyCozO2...), spinel oxides LiNixMn2-xO4 as well as olivine LiFePO4. Conversely, the selection of negative electrodes is mainly limited to graphite or Li4Ti5O12 (LTO). Graphite is inexpensive and delivers large capacity but suffers from the formation of solid electrolyte interphase (SEI) as well as Li dendrites formed at high rate, leading to low rate capability and security problems [1]. Li4Ti5O12 (LTO) on the other hand, is able to circumvent the problems of graphite thanks to its higher working potential (1.5 V vs Li+/Li) and minimal structural change during lithiation [2]. However, LTO has a lower energy density than graphite due to a higher working potential and a moderate specific capacity (∼150 mAh g− 1 and 120 mAh g− 1 at 1C and 5C rate, respectively). Therefore, there is a strong need of researching large-capacity insertion-based negative electrode materials working in the 1.0 < V ≤ 1.5 V voltage range to design new generation high energy density full cells.Transition-metal nitrides are considered to be among the most promising class of anode materials for LiBs [3]. Within this family, Li7MnN4 (LMN) [4] with an anti-fluorite 3D structure has received great attention due to its large specific capacity of 280 mAh g-1, excellent cycle stability and appropriate working potential of 1.2 V. We previously showed this material prepared at high temperature exhibits very large particle size [4]. Therefore, a crucial post-synthesis ball-milling step was required to benefit from the maximum capacity and high rate capability. However, this ball-milling step is hard to reproduce due to its dependence on many instrumental factors such as jar geometry, ball/material mass ratio [4].In this work, an optimization of the synthesis conditions of LMN is proposed and new key parameters controlling the particle size distribution (PSD) are identified, allowing the suppression of the post-synthesis ball-milling process. Thanks to the specific morphology attained when using our optimized synthesis conditions, the as-synthesized LMN material is able to deliver larger capacity at higher rate (265 mAh g− 1 and 160 mAh g− 1 at 1C and 5C rate, respectively). These capacity values are the best to our knowledge and compete with that of benchmark LTO. Furthermore, the lower working potential of LMN (1.2 V, i. e. 0.35 V lower than LTO) is expected to provide larger energy density in a full cell device compared to LTO.To carry this argument further, NMC/LMN full cell is constructed for the first time with LiNi0.6Mn0.2Co0.2O2 and pre-delithiated LMN (Li5.3MnN4). This NMC/LMN coin cell is applied for galvanostatic cycling at different current densities while a 3-electrode cell using metallic Li as reference electrode is used to clarify potential changes during the charge-discharge process. We show the NMC/LMN full cell replicates the electrochemical performance of NMC/Li half-cell in the 3.2 V - 2 V potential window. These results prove the feasibility and compatibility of the NMC/LMN full cell and the suitability of delithiated LMN as negative electrode material. Remarkably, the maximum energy density of the NMC/LMN full cell, of 256 Wh/kg(based on total active materials mass loading), is 30% to 50% higher than that exhibited by a NMC/LTO full cell.[1] T. Waldmann, B. I. Hogg, and M. Wohlfahrt-Mehrens, “Li plating as unwanted side reaction in commercial Li-ion cells – A review,” J. Power Sources, vol. 384, no. November 2017, pp. 107–124, 2018.[2] T. Ohzuku, A. Ueda, and N. Yamamoto, “Zero‐Strain Insertion Material of Li [ Li1 / 3Ti5 / 3 ] O 4 for Rechargeable Lithium Cells,” J. Electrochem. Soc., vol. 142, no. 5, pp. 1431–1435, 1995.[3] J. M. Tarascon and M. Armand, “Issues and challenges facing rechargeable lithium batteries,” Mater. Sustain. Energy A Collect. Peer-Reviewed Res. Rev. Artic. from Nat. Publ. Gr., vol. 414, no. November, pp. 171–179, 2010.[4] E. Panabière, N. Emery, S. Bach, J. P. Pereira-Ramos, and P. Willmann, “Ball-milled Li7MnN4: An attractive negative electrode material for lithium-ion batteries,” Electrochim. Acta, vol. 97, pp. 393–397, 2013. Figure 1

Methods for Estimating Composition of Single Walled Carbon Nanotubes Based on Electronic Type

— Synthesized single-walled carbon nanotubes (SWCNTs) consist of a mixture of chiralities and therefore a post-synthesis separation is essential to separate them based on electronic type i.e., metallic (m-SWCNT) or semiconducting (s-SWCNT) for device applications. A key parameter to measure the effectiveness of separation process is the enrichment composition percentage between m-SWCNT and s-SWCNT, which can be estimated via several methods based on optical characterizations. In this paper, we compare the composition percentage estimations from 3 different methods based on Raman spectroscopy and UV-Vis optical absorption spectroscopy. The estimation methods are radial breathing mode (RBM) peak analysis, optical absorption area under curve (OUA) and first derivative amplitude of the optical absorption curve (FDA). Four different SWCNT sources were used in this study, which were subjected to post-synthesis separation process via agarose gel chromatography. Raman and UV-Vis spectroscopy measurements were carried out on all samples, before and after separation. From the estimations, we observed firstly that there are some variations on the estimated enrichment compositions between different methods, although the values are comparable. Secondly, for some SWCNTs samples, only a certain estimation method showed reliable composition percentage. The results presented in this work may provide viable options for characterizations of SWCNTs as there is no direct method to quantify the absolute composition percentage of SWCNTs based on electronic type. Keywords—single-walledcarbon nanotube, separation, electronic type, optical characterization, purity percentage.

Tracing characteristic variations of cellulose nanocrystals during the post-synthesis purification process

Tracing characteristic variations of cellulose nanocrystals during the post-synthesis purification process

Room Temperature In-Situ Synthesis of Inorganic Lead Halide Perovskite Nanocrystals Sol Using Ultraviolet Polymerized Acrylic Monomers as Solvent and Their Composites with High Stability

As a kind of promising optoelectrical material, all-inorganic perovskite nanocrystals CsPbX3 (X = Cl, Br, I) have attracted much attention, due to their excellent optoelectrical characteristics, in recent years. However, their synthesis approaches require rigorous conditions, including high temperature, eco-unfriendly solvent or complex post-synthesis process. Herein, to overcome these issues, we reported a novel facile room temperature in-situ strategy using ultraviolet polymerizable acrylic monomer as solvent to synthesis CsPbX3 nanocrystals without a complex post-synthesis process. In this strategy, adequate soluble precursors of Cs, Pb and Br and reaction terminating agent 3-aminopropyltriethoxysilane (APTES) were used. The obtained CsPbBr3 nanocrystals showed a high photoluminescence quantum yields (PLQY) of 87.5%. The corresponding polymer composites, by adding light initiator and oligomer under ultraviolet light radiation, performed excellent stability in light, air, moisture and high temperature. The reaction process and the effect of the reaction terminating agent have been investigated in detail. This strategy is a universal one for synthesizing CsPbX3 nanocrystals covering visible light range by introducing HCl and ZnI2.

Improving Open-circuit Voltage in PbS-based QDPVs Using Different Pb Precursors

Lead sulfide (PbS) quantum dots (QDs) have been researched for photovoltaic (PV) applications for decades. A large open-circuit voltage (Voc) deficit to bandgap is one of the drawbacks to overcome in PbS QD-based photovoltaics (QDPVs) compared to other photovoltaic systems. Here, we report the Voc improvement using a different Pb-precursor, PbCl2, which is known to have an better native ligand for chemical stability and photoluminescence quantum yield. We synthesized appropriate size of PbS QDs for PV applications by the Cademartiri method with modification. The PbCl2 precursors used in the Cademartiri method supply chloride ions (Cl−) for the atomic passivation. The Cl− as a native atomic ligand is substituted to iodide ions (I−) through post-synthesis ligand exchange process, and the remaining Cl− as a PbClx shell layer still exists after ligand exchange and passivates the QD surface. The Voc using PbS QDs from the Cademartiri synthesis is 20% larger than that from the Hines synthesis.

Interplay between Activation Processes, Physicochemical Properties and Electrochemical Performance of “Core-Shell” Carbon Nitride Pt-Ni ORR Electrocatalysts Based on Hierarchical Graphene Supports

The sluggishness of the kinetics of the oxygen reduction reaction (ORR) is one of the most relevant phenomena curtailing the operation capability of proton-exchange membrane fuel cells (PEMFCs)[1]. Hence, the development of advanced ORR electrocatalysts (ECs) is one of the main goals of the research in this field. The ECs described here exhibit a “core-shell” morphology: a hierarchical graphene-based support (H-GR) “core” is covered by a carbon nitride “shell” stabilizing the active sites in “coordination nests” [2]. The “core” comprises highly defected graphene nanoplatelets [3] and carbon black nanoparticles; the latter act as spacers and facilitate the charge and mass transport phenomena that take place during the EC operation. The ECs proposed here are characterized by a very low loading of platinum, on the order of ca. 5 wt%, that is the “active metal”; Ni is introduced as the “co-catalysts” to improve the ORR performance [2]. An extensive post-synthesis activation process (A) is applied to the ECs, significantly affecting their chemical composition, structure and morphology. The ORR performance of the “activated” ECs is much improved in comparison with state-of-the-art Pt/C reference ECs. This work is aimed at investigating the effect of different activation parameters on the ORR performance and reaction mechanism, aiming at a robust and reliable upscaling of the preparation process [4]. The proposed ECs are extensively characterized both before and after A to study the complex interplay between the synthetic/activation parameters, the physicochemical properties, and the electrochemical ORR performance both “ex-situ” and in single PEMFC. The bulk chemical composition of the ECs is determined by means of Inductively-coupled plasma atomic emission spectroscopy (ICP-AES) and CHNOS microanalyses; the structure is investigated through wide-angle X-ray diffraction (WAXD) and vibrational spectroscopies (e.g., confocal micro-Raman); the surface composition and oxidation states are probed with X-ray photoelectron spectroscopy (XPS); morphology is observed by high-resolution transmission electron microscopy (HR-TEM); the details of the ORR performance and reaction pathway as a function of the pH of the environment are elucidated by cyclic voltammetry with the rotating ring-disk electrode (CV-TF-RRDE). Finally, the ECs are used to fabricate membrane-electrode assemblies (MEAs) that are tested in single PEMFC in operating conditions. Acknowledgement This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 785219, and from the BIRD 2018 program of UNIPD.

Study of the Thermal Stability of Faujasite Zeolite Synthesized from Kaolin Waste from the Amazon

The waste from the processing of kaolin in the Amazonian region of Brazil was subjected to a calcination process at 700°C for 2 h to obtain metakaolin, which, together with sodium hydroxide and sodium silicate, formed the reaction mixture. This mixture was subjected to an aging step (24 h at 60 rpm), and a subsequent hydrothermal process at 110°C for 10 h. By means of X-ray diffraction (XRD), differential thermal and thermogravimetric analysis (DTA/TG) and scanning electron microscopy (SEM) techniques, the crystallization of a single phase, faujasite (FAU) zeolite, was observed. In the postsynthesis process, it was verified by means of XRD that the thermal stability of this structure persists up to a temperature of 600°C. At 800°C, the structure of FAU collapses. Beginning at 850°C, new nepheline phases are formed, and at 1000°C, nepheline and mullite phases are formed.

Alveolar TiO2-β-SiC photocatalytic composite foams with tunable properties for water treatment

New alveolar TiO2-β-SiC photocatalytic composite foams gathering within a ready-to-use media, the TiO2 active phase and the β-SiC alveolar foam structure have been prepared through a Shape Memory Synthesis (SMS) replica method. They have been obtained by incorporating TiO2 powders inside the infiltration slurry used for transforming the pre-shaped polyurethane foam into its corresponding carbide. The photocatalytic composite foams contained 16 wt. % and 24 wt. % of TiO2, most of them being available for the reaction by being located in the external layer of the foam rather than dispersed within the foam matrix, so that no further post-synthesis immobilization process was needed for coating the foam with TiO2 active phase. The adsorption behaviour of the TiO2-β-SiC composite foams towards the Diuron pollutant in water was tuned by applying a final calcination treatment to the as-synthesized foams within the 400–700 °C range, that allowed to tune the amount of residual unreacted carbon within the foams, while allowing the formation of small TiO2 crystallites via the selective oxidation of TiC carbide, and thanks to the β-SiC resistance to oxidation. The TiO2-β-SiC composite foams calcined at 700 °C outperformed a reference β-SiC supported foam TiO2 catalyst in terms of diuron degradation, while the reference foam remained more efficient in terms of mineralization rate.

Investigation of the Influence of Nanostructured LiNi0.33Co0.33Mn0.33O2 Lithium-Ion Battery Electrodes on Performance and Aging

The paper focuses on the performance and aging behavior of lithium nickel cobalt manganese oxide commercial standard material (NCM-111) which is improved with a post synthesis process in order to enhance the cathode active material of lithium-ion pouch cells regarding their capacity and cyclic stability. The aging behavior of the cells is analyzed with electrochemical impedance spectroscopy (EIS) during long-term electrochemical load cycling tests based on the Common Artemis Driving Cycle (CADC). Additionally, post-mortem investigations using scanning electron microscopy (SEM) and X-ray diffraction (XRD) were performed. The results demonstrate that post-processing of electrode active material is an effective tool to improve the properties of lithium-ion electrode materials, especially regarding high energy applications and lifetime optimization. The paper bridges the gap between lithium-ion battery electrode material development and the necessary cell testing under automotive relevant conditions which is important for the evaluation of new lithium-ion battery materials for automotive applications.