Effects of hydroxyl radicals and oxygen species on the 4-chlorophenol degradation by photoelectrocatalytic reactions with TiO2-film electrodes

The supported nano-TiO₂ electrode was prepared by sol–gel and hydrothermal method, and the photoelectrocatalytic degradation of 4-chlorophenol (4-CP) under UV irradiation has been investigated to reveal the roles of hydroxyl radicals and dissolved oxygen species for TiO₂-assisted photocatalytic reactions. The degradation kinetics, the formation and decay of intermediates, the isotopic tracer experiments with H₂O¹⁸, the removal yield of total organic carbon and the formation of active radical species in the presence of oxygen or not were examined by HPLC, GC–MS, TOC and spin-trap ESR spectrometry. It was found that most of OH radicals in the primary hydroxylated intermediates derived from the oxidation of adsorbed H₂O or HO⁻ by photo-holes in the electrochemically assisted TiO₂ photocatalytic system. It also indicates that the enhancement in the separation efficiency of photogenerated charges by applying a positive bias (+0.5 V vs SCE) has little role in the following decomposition and mineralization of these hydroxylated intermediates in the absence of oxygen. According to above experimental results, the pathway of 4-CP photocatalytic degradation was deduced initially. Due to the combined effect of OH radicals and dissolved oxygen species, the hydroxylated 4-chlorphenol, via cis, cis-3-chloromuconic acid, was decomposed into low molecular weight acid and CO₂.     

An Unexplored O2‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO2 Photocatalysis: An Isotopic Probe Study

The aerobic decarboxylation of saturated carboxylic acids (from C₂ to C₅) in water by TiO₂ photocatalysis was systematically investigated in this work. It was found that the split of C¹? C² bond of the acids to release CO₂ proceeds sequentially (that is, a C₅ acid sequentially forms C₄ products, then C₃ and so forth). As a model reaction, the decarboxylation of propionic acid to produce acetic acid was tracked by using isotopic‐labeled H₂¹⁸O. As much as ≈42 % of oxygen atoms of the produced acetic acids were from dioxygen (¹⁶O₂). Through diffuse reflectance FTIR measurements (DRIFTS), we confirmed that an intermediate pyruvic acid was generated prior to the cut‐off of the initial carboxyl group; this intermediate was evidenced by the appearance of an absorption peak at 1772 cm^?1 (attributed to C?O stretch of α‐keto group of pyruvic acid) and the shift of this peak to 1726 cm^?1 when H₂¹⁶O was replaced by H₂¹⁸O. Consequently, pyruvic acid was chosen as another model molecule to observe how its decarboxylation occurs in H₂¹⁶O under an atmosphere of ¹⁸O₂. With the α‐keto oxygen of pyruvic acid preserved in the carboxyl group of acetic acid, ≈24 % new oxygen atoms of the produced acetic acid were from molecular oxygen at near 100 % conversion of pyruvic acid. The other ≈76 % oxygen atoms were provided by H₂O through hole/OH radical oxidation. In the presence of conduction band electrons, O₂ can independently accomplish such C¹? C² bond cleavage of pyruvic acid to generate acetic acid with ≈100 % selectivity, as confirmed by an electrochemical experiment carried out in the dark. More importantly, the ratio of O₂ participation in decarboxylation increased along with the increase of pyruvic acid conversion, indicating the differences between non‐substituted acids and α‐keto acids. This also suggests that the O₂‐dependent decarboxylation competes with hole/OH‐radical‐promoted decarboxylation and depends on TiO₂ surface defects at which Ti_4c sites are available for the simultaneous coordination of substrates and O₂.     

Multiblock copolymers composed of poly(butylene succinate) and poly(1,2-propylene succinate): Effect of molar ratio of diisocyanate to polyester-diols on crosslink densities, thermal properties, mechanical properties and biodegradability

In order to study the relationship between structure and properties, multiblock copolymers composed of poly(butylene succinate) (PBS) and poly (1,2-propylene succinate) (PPSu) have been synthesized by chain-extension at various molar ratios of hexamethylene diisocyanate (HDI) to polyester-diols, which have been abbreviated as R-values in this paper. Molecular weights of soluble fractions, gel fractions and crosslink densities have been determined. Thermal properties, mechanical properties and biodegradability have been studied and correlated with R-values. Crystallization of copolymers becomes difficult with increasing R-value. Tensile strength, flexural strength and flexural modulus tend to increase with increasing R-value up to 1.2, and vary little when R-value increases from 1.2 to 1.3, then decrease with further increase in R-value. Impact strength achieves a maximum value at R-value of 1.3. Biodegradation rate reaches a minimum value when R-value is 1.1. Biodegradation has been studied systematically by attenuated total reflectance Fourier transform infrared (ATR-FTIR), ¹H NMR and SEM.     

Ab initio study of the bonding and elastic properties of Ti2CdC

The chemical bonding and elastic properties of Ti₂CdC were investigated by means of a first-principles pseudopotential total energy method. The calculated results for the lattice constants and internal coordinate agree with experimental values very well. Ti₂CdC is conducting, and the Cd-d states have little effect on the chemical bonding. The elastic properties were estimated from the individual elastic constants by Voigt approximation. The calculated shear-modulus of Ti₂CdC, 70 GPa, is the lowest value among all MAX phases. The lower shear-modulus and shear-modulus-to-bulk-modulus ratio are related to the weaker Ti–Cd bond, which indicates the lower coefficient of friction. This suggests that Ti₂CdC would be a potential electrical frictional material.     

四元淋洗液的离子色谱法同时分离和测定铁(Ⅲ)、铁(Ⅱ)、铜(Ⅱ)、镍(Ⅱ)、锌(Ⅱ)、钴(Ⅱ)和铅(Ⅱ)

本文叙述了一种四元淋洗液同时分离和测定七种金属离子的色谱条件。探讨了各离子的保留行为与淋洗液pH值和络合剂浓度间的变化规律。方法用于镀铬槽液中金属杂质分析,相对标准偏差小于2.0％,相对误差不超过3.5％。     

生物质石墨烯/LaFeO3纳米复合材料的光催化活性

采用两步法制备生物质石墨烯/LaFeO3纳米复合材料(石墨烯加入量分别为LaFeO3的1;、3;、5;、7;),应用差热-热重分析、X射线衍射(XRD)、扫描电子显微镜(SEM)等测试手段对生物质石墨烯/LaFeO3纳米复合材料样品的物相及微观结构进行了表征;采用傅里叶变换红外光谱仪对样品进行了红外分析(FTIR);研究了生物质石墨烯加入量对生物质石墨烯/LaFeO3复合材料降解亚甲基蓝光催化降解率的影响.结果 表明:通过两步法所制备的生物质石墨烯/LaFeO3纳米光催化剂稳定性好,具有高效光催化活性;生物质石墨烯的加入提高了LaFeO3对亚甲基蓝的光催化降解率;采用175W荧光高压汞灯光照30 min时,加入7;生物质石墨烯的LaFeO3样品对亚甲基蓝的光催化降解率最高达到56;,比纯LaFeO3光催化降解率高出50;.     

Grafted copolymer micelles with pH triggered charge reversibility for efficient doxorubicin delivery

The instability and premature charge reversal at pH 7.4 have become the major limitations of charge‐reversal delivery systems. To address this problem, graft copolymer of poly(butylene succinate)‐g‐cysteamine‐bi‐poly(ethylene glycol) (PBS‐g‐CS‐bi‐PEG, bi = benzoic imine bond) was designed and synthesized through facile thiol‐ene click reaction and subsequent Schiff's base reaction. Then, PBS‐g‐CS‐bi‐PEG and carboxyl‐functionalized polyester of poly(butylene succinate)‐g‐3‐mercaptopropionic acid (PBS‐g‐MPA) co‐assemble in aqueous solution to give PEG shell‐sheddable charge‐reversal micelles with sizes of 85–103 nm and low polydispersity of 0.11–0.12. Interestingly, the PBS‐g‐MPA/CS‐bi‐PEG micelles could sensitively and arbitrarily switch their surface charges between negative and positive status in response to pH fluctuation via reversible protonation and deprotonation of carboxyl and amino groups, which endows the desired stability of co‐assembly micelles either during long‐term storage or under physiological conditions. Doxorubicin (DOX) was loaded into PBS‐g‐MPA/CS‐bi‐PEG micelles with a high drug‐loading content of 10.2% and entrapment efficiency of 68% as a result of electrostatic attraction. In vitro release studies revealed that less than 25% of DOX was released within 24 h in the environment mimicking the physiological condition, whereas up to 81% of DOX was released in 24 h under weak‐acid condition resembling microenvironment in endosome/lysosome. In vitro cytotoxicity study suggested that blank PBS‐g‐MPA/CS‐bi‐PEG micelles possessed excellent biocompatibility, while DOX‐loaded PBS‐g‐MPA/CS‐bi‐PEG micelles showed significant cytotoxicity with half‐maximal inhibitory concentration (IC₅₀) of 1.55–1.67 μg DOX equiv/mL. This study provides a facile and effective approach for the preparation of novel charge‐reversal micelles with switchable charges and excellent biocompatibility, which are highly promising to be used as safe nanocarriers for efficient intracellular drug delivery. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2036–2046