Ligand-assisted cation-exchange engineering for high-efficiency colloidal Cs1−xFAxPbI3 quantum dot solar cells with reduced phase segregation

The mixed caesium and formamidinium lead triiodide perovskite system (Cs1−xFAxPbI3) in the form of quantum dots (QDs) offers a pathway towards stable perovskite-based photovoltaics and optoelectronics. However, it remains challenging to synthesize such multinary QDs with desirable properties for high-performance QD solar cells (QDSCs). Here we report an effective oleic acid (OA) ligand-assisted cation-exchange strategy that allows controllable synthesis of Cs1−xFAxPbI3 QDs across the whole composition range (x = 0–1), which is inaccessible in large-grain polycrystalline thin films. In an OA-rich environment, the cross-exchange of cations is facilitated, enabling rapid formation of Cs1−xFAxPbI3 QDs with reduced defect density. The hero Cs0.5FA0.5PbI3 QDSC achieves a certified record power conversion efficiency (PCE) of 16.6% with negligible hysteresis. We further demonstrate that the QD devices exhibit substantially enhanced photostability compared with their thin-film counterparts because of suppressed phase segregation, and they retain 94% of the original PCE under continuous 1-sun illumination for 600 h

Molecular discovery of half-metallic one-dimensional metal-organic framework

The metal-organic framework (MOF) is a large family of nanomaterials with tunable structural and electronic properties. Discovering half-metallic MOF can broaden the selection pool of half-metals for specific applications in the areas of electronics and catalysis. In this study, seven one-dimensional first-row transition metal-dithiolene MOFs have been systematically investigated using the first-principles density functional theory method. Our theoretical outcomes reveal that the electrical conductivities of these MOFs are determined by the electronic configurations of the metal cations. They can change from a semiconductor to a half-metal and further to a metal as the atomic number increases. Among all MOFs we considered, Cr(III)/Mn(III)/Fe(III)/Co(III)-dithiolene MOFs are promising candidates for spintronic applications.</p

Modeling of protein breakthrough performance in cryogel columns by taking into account the overall axial dispersion.

A model considering the overall axial dispersion for describing protein adsorption and breakthrough in monolithic cryogel beds has been developed. The microstructure of cryogels was characterized by tortuous capillaries with a normal diameter distribution but a constant pore wall thickness. The axial dispersion within cryogel columns was described by using the overall axial dispersion coefficient, which can be easily obtained by matching the experimental breakthrough curves without adsorption or measuring residence time distributions (RTDs). Experimental breakthrough curves of lysozyme within a metal-chelated affinity cryogel by Persson et al. (Biotechnol. Bioeng. 2004, 88, 224-236) and a cation-exchange cryogel by Yao et al. (J. Chromatogr. A 2007, 1157, 246-251) were employed as examples to test the model. The results showed that by using the axial dispersion coefficient and assuming uniform radial concentration profile at a given cross-section of the cryogel along the bed height, the model can describe the detailed behaviors of the in-bed overall axial dispersion, the in-pore mass transfer, as well as the protein adsorption and breakthrough. For a known overall axial dispersion coefficient, the lumped parameter of the mass transfer coefficient between the bulk liquid and the capillary wall can be determined by fitting the protein breakthrough curve at a known chromatographic condition. Once this parameter is determined, the model can be used to predict the protein breakthrough profiles under different conditions based on the basic physical parameters of the cryogel bed and the properties of the fluid and protein. The effective capillary diameters employed in the model are close to the actual pore sizes observed from the images by SEM. The model predictions of lysozyme breakthrough profiles at various flow rates are also in good agreement with the experimental data in both the metal-chelated affinity and cation-exchange cryogel columns

Pre-treatments for enhanced biochemical methane potential of bamboo waste

Various pre-treatments (acid, alkaline, enzyme and alkaline aided enzyme also termed combined) were evaluated on different fractions of bamboo waste from a chopstick production factory. Chemical oxygen demand (COD) solubilisation, monomeric/dimeric sugar yield, methane yield enhancement and methane production rate were assessed. The biochemical methane potential was determined in batch assays under mesophilic conditions (37 1 C) using the Automatic Methane Potential Test System (AMPTS-II). Pre-treatments led to enhanced COD solubilisation as compared to raw sample. Alkaline aided enzymatic pre-treatment led to the highest sugar yield, comparable to the theoretical yield. However, high sugar yield did not translate to high methane yield. The best pre-treatment in terms of methane yield was alkaline pre-treatment which resulted in a surplus of up to 88% methane yield. There was a positive correlation between dissolved COD and methane yield. Methane yield and methane production rate also increased with decreasing particle sizes. In all investigated scenarios, pre-treatment led to an improved methane production rate as compared to the raw samples. These results demonstrated that alkaline pre-treatment at ambient temperature was an efficient treatment option to improve methane yield of bamboo waste. (C) 2013 Elsevier B.V. All rights reserved

The Role of Steps on Silver Nanoparticles in Electrocatalytic Oxygen Reduction

Hydrogen fuel cell technology is an essential component of a green economy. However, it is limited in practicality and affordability by the oxygen reduction reaction (ORR). Nanoscale silver particles have been proposed as a cost-effective solution to this problem. However, previous computational studies focused on clean and flat surfaces. High-index surfaces can be used to model active steps presented in nanoparticles. Here, we used the stable stepped Ag(322) surface as a model to understand the ORR performance of steps on Ag nanoparticles. Our density functional theory (DFT) results demonstrate a small dissociation energy barrier for O2 molecules on the Ag(322) surface, which can be ascribed to the existence of low-coordination number surface atoms. Consequently, the adsorption of OOH* led to the associative pathway becoming ineffective. Alternatively, the unusual dissociative mechanism is energetically favored on Ag(322) for ORR. Our findings reveal the importance of the coordination numbers of active sites for catalytic performance, which can further guide electrocatalysts’ design.</p