RESUMEN
Certified reference materials (CRMs) with high accuracy and traceability play a significant role in the calibration of equipment and validation of analytical methods. However, there is still a lack of suitable solid waste CRMs for quality assurance and quality control. Thus, a CRM (GBW(E)085538) was developed for accurate determination and reliable measurement of the leaching of Pb and Zn in solid waste according to the requirements of ISO 17034 and the recommendations of ISO Guide 35. This study describes the steps performed for the development of the CRM. These steps include material preparation, homogeneity, and stability during transport and storage, assignment of certified values, and their uncertainties. The material was dried, ground, sieved and well-mixed, and the final bulk material was bottled in 1 kg portions. Analytical techniques like inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma-optical emission spectrometry (ICP-OES), and flame atomic absorption spectrometry (AAS) have been used for the characterization of property values. Concurrently, an inter-laboratory comparison study involving 9 qualified laboratories was implemented to support the certification study. The certified values of Pb and Zn were (4.66 ± 0.21) mg/L and (2.95 ± 0.14) mg/L with 7-month stability.
RESUMEN
High-efficiency red room-temperature phosphorescence (RTP) emissions have been achieved by embedding carbon dots (CDs) in crystalline Mn-containing open-framework matrices. The rationale of this strategy relies on two factors: 1)â the carbon source, which affects the triplet energy levels of the resulting CDs and thus the spectral overlap and 2)â the coordination geometry of the Mn atoms in the crystalline frameworks, which determines the crystal-field splitting and thus the emission spectra. Embedding the carbon dots into a matrix with 6-coordinate Mn centers resulted in a strong red RTP with a phosphorescence efficiency of up to 9.6 %, which is higher than that of most reported red RTP materials. The composite material has an ultrahigh optical stability in the presence of strong oxidants, various organic solvents, and strong ultraviolet radiation. A green-yellow RTP composite was also prepared by using a matrix with 4-coordinate Mn centers and different carbon precursors.
RESUMEN
Zeolites are an important class of tetrahedrally coordinated inorganic materials that have been widely used in many chemical industries as catalysts, adsorbents, and ion-exchangers. To date, over 200 types of zeolite framework have been discovered. Predicting not-yet-discovered zeolite frameworks is of great importance not only for zeolite structure determination but also for the identification of promising synthetic candidates with desirable functions. However, owing to the complexity and diversity of zeolite framework topologies, zeolite structure prediction has been a challenging task for several decades. Many efforts have been devoted towards this end, among which the computer-aided assembly of zeolite framework constituent atoms (T atoms) in predefined Wyckoff positions (WPs) is a promising approach because of its high efficiency in configuration space searching. However, this approach suffers from high computational overheads caused by the large number of possible WP combinations. On the basis of the analysis of known zeolite structures, we find that the site symmetries of many WPs are incompatible with the tetrahedral coordination of T atoms. Moreover, to avoid the formation of chemically unfeasible distorted tetrahedral coordination, T atoms cannot be too "crowded" in some WPs. We define, for the first time, the T atom distribution (TAD) densities for special site symmetries as the numbers of T atoms per special point, per unit length of rotation axes, or per unit area of mirror planes, respectively. By restricting the number of T atoms in every WP so as not to exceed the highest allowed TAD density, WP combinations for zeolite structure prediction can be reduced by 1-4 orders of magnitude. Taking advantage of this discovery, the efficiency of zeolite structure prediction based on the enumeration of WP combinations can be significantly improved.
