Hong-Chang Yao

Indirect Z-Scheme BiOI/g-C3N4 Photocatalysts with Enhanced Photoreduction CO2 Activity under Visible Light Irradiation

Rational design and construction of Z-scheme photocatalysts has received much attention in the field of CO2 reduction because of its great potential to solve the current energy and environmental crises. In this study, a series of Z-scheme BiOI/g-C3N4 photocatalysts are synthesized and their photocatalytic performance for CO2 reduction to produce CO, H2 and/or CH4 is evaluated under visible light irradiation (λ > 400 nm). The results show that the as-synthesized composites exhibit more highly efficient photocatalytic activity than pure g-C3N4 and BiOI and that the product yields change remarkably depending on the reaction conditions such as irradiation light wavelength. Emphasis is placed on identifying how the charge transfers across the heterojunctions and an indirect Z-scheme charge transfer mechanism is verified by detecting the intermediate I3(-) ions. The reaction mechanism is further proposed based on the detection of the intermediate (•)OH and H2O2. This work may be useful for rationally designing of new types of Z-scheme photocatalyst and provide some illuminating insights into the Z-scheme transfer mechanism.

Enhanced Photoreduction CO2 Activity over Direct Z-Scheme α-Fe2O3/Cu2O Heterostructures under Visible Light Irradiation

Hematite-cuprous oxide (α-Fe2O3/Cu2O) nanocomposites are synthesized based on the design of Z-scheme photocatalyst for CO2 reduction. The band structure for the typical Fe2O3/Cu2O (with 1:1 mole ratio) is characterized by UV-vis reflectance spectroscopy and X-ray/ultraviolet photoelectron spectroscopy, and its heterojunction is determined to be Type II band alignment. The photoreduction CO2 activities of the heterostructures are investigated in the presence of water vapor. The CO yields are changed with Fe/Cu mole ratio, and the maximal CO yield attains 5.0 μmol·g cat(-1) after 3 h of visible-light irradiation. Besides the effect of light wavelength, H2O/CO2 molar ratio and temperature on the products is studied. The selectivity of the prepared catalysts is tunable by modulating the light wavelength. The reaction mechanism is proposed and further confirmed experimentally. The results gained herein may provide some insights into the design of Z-scheme photocatalysts for CO2 reduction.

Synergistic photocatalysis of Cr(VI) reduction and 4-Chlorophenol degradation over hydroxylated α-Fe2O3 under visible light irradiation.

A series of Fe2O3 materials with hydroxyl are synthesized in different monohydric alcohol (C2-C5) solvents by solvothermal method and characterized by XRD, BET, XPS, TG and EA. The amount of hydroxyl is demonstrated to be emerged on the surface of the as-synthesized Fe2O3 particles and their contents are determined to be from 7.99 to 3.74 wt%. The Cr(VI) reduction experiments show that the hydroxyl content of Fe2O3 samples exacts great influence on the photocatalytic activity under visible light irradiation (λ>400 nm) and that the Fe2O3 sample synthesized in n-butyl alcohol exhibits the optimal photocatalytic activity. The synergistic photocatalysis for 4-Chlorophenol (4-CP) degradation and Cr(VI) reduction over above Fe2O3 sample is further investigated. The photocatalytic ratio of Cr(VI) reduction are enhanced from 24.8% to 70.2% while that of 4-CP oxidation are increased from 13.5% to 47.8% after 1 h visible light irradiation. The Fe2O3 sample keeps good degradation rates of mixed pollutants after 9 runs. The active oxygen intermediates O2(-)˙, ˙OH and H2O2 formed in the photoreaction process are discovered by ESR measurement and UV-vis test. The photocatalytic degradation mechanism is proposed accordingly.

Anion exchange induced tunable catalysis properties of an uncommon butterfly-like tetranuclear copper(II) cluster and magnetic characterization

An uncommon butterfly-like tetranuclear copper(ii) cluster with the formula {[Cu(4)(μ(3)-OH)(2)(μ(4)-Cl)(H(2)O)(2)(L)(2)]·Cl(H(2)O)(7)}(n) (1) (H(2)L = 1,2-bis[3-(1,2,4-triazolyl)-4-amino-5-carboxylmethylthio]ethane) has been synthesized. Compound 1 exhibits interesting anion exchange characteristics, in which both guest and coordinated Cl(-) can be replaced by I(-) or NO(3)(-) in water. Furthermore, a high catalytic selectivity to produce poly(phenylene ether) by the oxidative coupling of 2,6-dimethylphenol in water is found to be 74% for 1 and 87% for the anion-exchanged product 1-MI(x), respectively. Additionally, the antiferromagnetic interaction among Cu ions for compound 1 is also found.

Metal–organic Coordination Polymers Assembled from Divalent Transition Salts with a Flexible Spacer Ligand: Hydrothermal Syntheses, Crystal Structures, and Luminescent and Magnetic Properties

Seven new metal-organic coordination polymers, [M(tzda)(H2O)4] n [M = Co(1), Ni (2) and Zn(3)], [Zn(tzda)(4,4′-bipy)] n (4), [Cd(tzda)(4,4′-bipy)0.5(H2O)] n (5) and [M(tzda)(4,4′-bipy)(H2O)] n [M = Co(6), Ni(7)] [H2tzda = (1,3,4-thiadiazole-2,5-diyldithio)diacetic acid, 4,4′-bipy = 4,4′-bipyridine] have been hydrothermally synthesized and structurally characterized by X-ray single crystal diffraction. Compounds 1–3 display similar 1D zigzag chain structure. Compound 4 possesses a 2D-layered architecture generated from [Zn(tzda)] n moiety with double-chain structure cross-linking 4,4′-bipy spacers, while compound 5 consists of –Cd–OCO–Cd–OCO– chains cross-linked through –CH2SC2N2SSCH2– spacers of tzda anions and 4,4′-bipy, also showing a 2D-layered structure. The structures of 6 and 7 seem more complicated, in which the [M(tzda)] n layered subunits are extended to unique 3D framework by the bridging 4,4′-bipy ligand. Photoluminescence investigations reveal that 4 and 5 both display strong blue emissions in the solid state at room temperature, which could be significant in the field of luminescent materials. The magnetic studies of 6 and 7 show both display the characteristics of a weak antiferromagnetic coupling between metal ions in the system mediated by carboxylate bridges.

Syntheses, structures, and characterizations of two coordination polymers assembled from zinc(II) salts with 1,2-bis[3-(1,2,4-triazolyl)-4-amino-5-carboxylmethylthio]ethane

Two new coordination polymers, [ZnL] n (1) and {[Zn(phen)(L)(H2O)] · 3H2O} n (2) (H2L = 1,2-bis[3-(1,2,4-triazolyl)-4-amino-5-carboxylmethylthio]ethane, phen = 1,10-phenanthroline), have been synthesized and characterized by elemental analysis, IR, and X-ray diffraction. Polymer 1 is a 1-D infinite chain (space group P 1) and further forms a 3-D supramolecular structure by S ··· S interactions and hydrogen bonds. Polymer 2 displays a mononuclear structure (space group P 1) and extends into a 3-D supramolecular structure through hydrogen bonds. In addition, spectra and thermal stability of 1 and 2 are also discussed. Strong luminescence characteristics of both polymers are found, suggesting their potential applications as luminescent materials.

Preparation of ultrafine silica powders

Numerous processes have been used for the preparation of ultrafine silica powders, which include the flame or plasma hydrolysis of silicon tetrachloride vapor at high temperatures [1, 2] and the hydrolytic polycondensation of organosilicates or silicon tetrachloride in liquid solvents [3, 4]. Silica powders produced by the above methods have unique properties such as fine particle size, large surface area and good dispersibility. However, their high production costs have limited the powders’ large-scale commercial applications [5]. Development of alternative cheaper routes to produce ultrafine silica powders with desirable characteristics is therefore of considerable interest. In this letter, we report the preparation of ultrafine silica powders by sol-gel process from water glass using ethyl acetate as a latent acid reagent. The interaction of ethyl acetate with water glass solution and the gelling characteristic of water glass in the presence of ethyl acetate were examined and the effect of calcination on the properties of the silica powders was studied. Water glass (technical grade) with SiO2 content of 26.4% and SiO2/Na2O mole ratio of 3.3 was used as a starting material, which was diluted with distilled water and vacuum filtered before use. Ethyl acetate (analytical grade) was added to water glass solution in a given mole ratio of CH3COOC2H5 to SiO2 under stirring at 25 ± 1◦C. After reaction for a period of time and appearance of silica gels, the resulting slurry was kept reacting for 40 min, and then acidified by HCl and stirred for another 1 h at 80 ◦C. It was filtered at the pump and thoroughly washed with distilled water to eliminate Cl− and Na+ ions. The wet gels obtained after filtration were stirred with n-butanol and distilled to remove water as azeotrope. Ultrafine silica powders can be obtained after azeotropic distillation and drying at 120 ◦C for 2 h. The calcination of the powders was carried out at 300 to 1200 ◦C for 2 h with an air atmosphere. The pH of the reaction system was monitored by using a pH meter (Model pHS2, Shanghai, China). The hydrolysis ratio of ethyl acetate was obtained by determining the content of alcohol generated in the process of gelling reaction via gas chromatography (Model BF3400, Beijing, China). The conditions were as follow: column, GDX-103, 2.6 mm × 2 m, 60–80 mesh; detector, TCD; carrier gas, He, volume rate, 45 mL/min; column temperature, 120 ◦C; inject and detection temperature, 210 ◦C. A series of sols and gels were prepared to examine the change in gelation time with the mole ratio of CH3COOC2H5 to SiO2. The gelation time of the reaction system was defined as the time when a visible solid phase was detected either in the form of a gel or precipitate. In this system gels were only formed at low ethyl acetate contents, whereas at higher contents phase separation of the solid and liquid phase occurred. This gelation time was a useful qualitative measure of the stability of the reaction system. The particle morphology and size of the silica sols and silica powders were observed by transmission electronic microscopy (TEM) (Model H-600, Hitachi, Tokyo, Japan). Specimens were made by dropping the silica sols and the prepared water suspension, including silica powders, onto carbon filmed copper grids. The phase structure of the silica powders was determined by X-ray diffractometry (Model D/MAX-III B, Rigaku Co., Tokyo, Japan) with Cu Kα radiation. The specific surface areas of the as-synthesized and calcined powders were measured via the Brunauer-Emmett-Teller (BET) method with nitrogen absorption using an automated volumetric analyzer (Model ASAP 2000, Micromeritics). In the solution of water glass, silica is present as monomeric, oligomeric and polymeric colloidal silicate ions. The colloidal species, with particles in the range 1 to 2 nm, are in equilibrium with monomeric and oligomeric species [6]. The behavior of silicates in solution is governed by the two following interdependent sets of equilibria [7]:

Synthesis of fluorescent polymeric carbon nitride quantum dots in molten salts for security inks

Polymeric carbon nitride quantum dots (CNQDs) with an average size of approximately 2.5 nm were prepared directly from melamine via a one-step molten salt method. The formation mechanism and photoluminescence (PL) properties of the resulting CNQDs were investigated by means of TEM, XRD and PL spectroscopy. The CNQDs can be dispersed in water to form a transparent colloidal solution and emit blue PL with excellent photostability. Interestingly, upon addition of CuCl2 and NaHCO3 in turn, the PL of CNQDs can be turned off and on accordingly. Taking advantage of the on–off–on PL response, the CNQDs can be used as a fluorescent security ink for information coding, encryption and decryption, indicating their promising application in data security and high-level anti-counterfeiting fields.