[Determination of Bi in Soils and Sediments by Atomic Fluorescence Spectrometry].

A method for determination of the contents of Bi in soils and sediments by atomic fluorescence spectrophotometry (AFS) was established by using aqua regia as the dissolved medium. In this paper, the instrument parameters, load flow and reducing agent concentration were optimized. Compared with microwave digestion and electric heating plate digestion, water bath digestion demonstrated the better digestion efficiency and was most commonly used. Under the optimal experimental conditions, the detection limit (LOD) was 0.01 mg·kg-1 (sample quantity 0.500 0 g, sample volume 50 mL), and the limit of quantitation (LOQ) was 0.04 mg·kg-1. The results were in good agreement with the centified value, and the relative error was -4.7%~-2.0%. For determination of soil and sediment actual samples, the relative standard deviation (RSD) were 2.5%~3.4% and 3.1%~3.4%, respectively, and the recoveries of the method respectively ranged from 97.6%~102% and 99.5%~104%.

Determination of Beryllium in Soil and Sediment by Graphite Furnace Atomic Absorption with a Microwave-Acid Digestion Method.

A method for determination of beryllium in soils and sediments by microwave-acid digestion/graphite furnace atomic absorption (GFAA) is described. In this paper, the working conditions of the instrument are optimized, the drawing of calibration curve is expounded, the pretreatment process of soil and sediments (including microwave heating process and the selection of digestion system) is discussed, and the interference of coexisting elements is examined. The sample was pretreated by microwave digestion parameters using HNO3/ HCl/HF mixed acid system. The method is fast and simple without matrix modifier, and has no interference by coexisting ions, and has high repeatability and reproducibility. Under the optimal experimental conditions, the limit of detection (LOD) is 0.004 9 mg · kg⁻¹ (sample quantity 0.200 0 g, sample volume 25 mL), and the limits of quantitation (LOQ) is 0.20 mg · kg⁻¹. This method is used to measure the standard samples and actual samples, whether in the laboratory, or between laboratories, has good accuracy and precision.

Donor-acceptor moiety functionalized covalent organic frameworks for boosting charge separation and H2 photogeneration.

Covalent organic frameworks (COFs) have a broad prospect to be used as a photocatalytic platform to convert solar energy into valuable chemicals due to their tunable structures and rich active catalytic sites. However, constructing COFs with tuned sp2-carbon donor-acceptor moiety remains an enormous challenge. Herein, we synthesized two new fully π-conjugated cyano-ethylene-linked COFs containing benzotrithiophene as functional group by Knoevenagel polycondensation reaction. The accetpor 2,2'-bipyridine unit in BTT-BpyDAN-COF skeleton favored the formation of a intermolecular specific electron transport pathway with the donor benzotrithiophene, and thereby promoted charge separation and transfer efficiency. Specifically, a donor-acceptor (D-A) type BTT-BpyDAN-COF exhibited high hydrogen evolution rate of 10.1 mmol g-1h-1 and an excellent apparent quantum efficiency of 4.83 % under visible light irradiation.

Recent advances on covalent organic frameworks (COFs) as photocatalysts: different strategies for enhancing hydrogen generation.

The excessive use of traditional fossil fuels has led to energy and environmental pollution problems. Solar-driven hydrogen generation has attracted much attention in recent years owing to its environmental friendliness and economic feasibility. So far, a series of photocatalysts have been advanced. Unfortunately, these photocatalysts face some issues including poor sunlight harvesting ability, weak photo-corrosion resistance, broad band gap, bad stability, inferior hydrogen evolution rate and so on. It just so happens that COFs have emerged to provide an opportunity for settling these issues. Covalent organic frameworks (COFs), a novel family of porous materials with regular porosity and tunable physicochemical structures, have been extensively explored as photocatalysts for hydrogen production. Moreover, their photocatalytic activities are highly structurally dependent. In this review, we mainly focus on the linkage chemistry and disparate strategies for boosting COF-based photocatalytic hydrogen generation performance in detail. The prospects and obstacles confronted in the development of COF-based photocatalysts and proposals to settle dilemmas are also discussed.