Enhance photocatalytic properties of TiO2 using π-π* conjugate system

Abstract

A novel π-π* conjugate system photo-catalyst was successfully constructed using aniline, pyrrole and TiO₂. The structures of photo-catalyst were measured by XRD, SEM, BET, TEM, FT-IR, XPS and TGA in detail. The photocatalytic properties were investigated in rhodamine B and methyl orange solution, respectively. And the enhance mechanism of π-π* conjugate system was discussed in depth. The weight percentage of Ti weight about 47% in the compound and the π-π* conjugate system did not change the crystal structure of TiO₂. The photocatalytic degradation properties of the π-π* conjugate system photo-catalyst could get 99% for rhodamine B and methyl orange after 10 and 15?min, respectively. The introduction of the π-π* conjugate system into TiO₂ was beneficial to improve light harvest, photoelectric response and separation of electron-holes.     

新型复合电极对偶氮染料分子的光催化降解

介绍了具有合成H2 O2 和光催化性能的双功能新型复合电极 ,并用X射线衍射、扫描电镜等方法进行了表征 .双功能复合电极是将TiO2 光催化剂负载在活性碳 (AC)和具有合成H2 O2 性能的新型载体空气电极上形成的 .在复合电极作阴极的光反应器中 ,·OH和TiO2 光催化剂的存在实现了光化学氧化与光催化氧化在同一电极 /溶液界面上的联合作用 .实验结果表明 ,复合电极对提高偶氮染料分子活性艳红 (K 2BP)的氧化降解速度起了重要作用 ,仅反应 3min ,脱色率可达 4 9% ;反应 80min ,偶氮染料分子COD去除率可达 4 7% .     

Synthesis, characterization and degradation of Bisphenol A using Pr, N co-doped TiO2 with highly visible light activity

Praseodymium and nitrogen co-doped titania (Pr/N-TiO₂) photocatalysts, which could degrade Bisphenol A (BPA) under visible light irradiation, were prepared by the modified sol-gel process. Tetrabutyl titanate, urea and praseodymium nitrate were used as the sources of titanium, nitrogen and praseodymium, respectively. The resulting materials were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV-vis absorbance spectroscopy, X-ray photoelectron spectroscopy (XPS), N₂ adsorption-desorption isotherm and Fourier transform infrared spectra (FTIR). It was found that Pr doping inhibited the growth of crystalline size and the transformation from anatase to rutile. The degradation of BPA under visible light illumination was taken as probe reaction to evaluate the photo-activity of the co-doped photocatalyst. In our experiments, the optimal dopant amount of Pr was 1.2 mol% and the calcination temperature was 500 °C for the best photocatalytic activity. Pr/N-TiO₂ samples exhibited enhanced visible-light photocatalytic activity compared to N-TiO₂, undoped TiO₂ and commercial P25. The nitrogen atoms were incorporated into the crystal of titania and could narrow the band gap energy. Pr doping could slow the radiative recombination of photogenerated electrons and holes in TiO₂. The improvement of photocatalytic activity was ascribed to the synergistic effects of nitrogen and Pr co-doping.     

Hydrothermal synthesis of C-doped Zn3(OH)2V2O7 nanorods and their photocatalytic properties under visible light illumination

A visible light-driven photocatalyst, C-doped Zn₃(OH)₂V₂O₇, prepared by a hydrothermal method was studied. The as-prepared catalyst was characterized by SEM, XRD, DRS, and XPS, and exhibited efficient photocatalytic activity in the degradation of methylene blue (MB) under visible-light irradiation. Besides decoloring, the decomposition of MB was also observed, further demonstrating the performance of the photocatalyst. The carbon existing on the surface of Zn₃(OH)₂V₂O₇ nanorods was free and in carbide form. Dye degradation followed first-order kinetics, and was explained on the basis of the Langmuir-Hinshelwood mechanism.     

微波辅助离子液体中锌-铁共掺杂纳米TiO_2光催化剂的制备及其光催化活性

在[Bmim]PF_6离子液体介质中,用微波于燥的方法制备了锌-铁共掺杂纳米TiO_2(TiO_2-Zn-Fe)光催化剂;并以甲基橙为模拟污染物,紫外灯为光源,考察了离子液体加入量、锌-铁掺杂量、微波干燥功率、微波干燥时间、煅烧温度、煅烧时间等因素对TiO_2-Zn-Fe光催化活性的影响.结果表明,掺杂物质硝酸锌和硝酸铁与钛酸丁酯的物质的量比分别为n(Zn)/n(Ti)=0.25%和n(Fe)/n(Ti)=0.005%时,在家用微波炉中于210W功率下干燥17.5min,再在高温箱式电阻炉中于540℃下煅烧处理1.5h,得到的TiO_2-Zn-Fe光催化剂的活性明显优于单一掺杂的TiO_2-Zn或TiO_2-Fe以及未掺杂的纯TiO_2,在紫外光照60min及太阳光照3h条件下相应的甲基橙的降解率分别达99.8%和99.6%.     

Ultrahigh‐Density Plasmonic‐Nanoparticle‐Sensitized Semiconductor Photocatalysts Profit from Cooperative Light Harvesting and Charge Separation Processes: Experiments,Simulations, and Multifunctional Plasmonics

Here, a controlled synthesis of remarkable 3D photocatalysts is presented that is composed of ultrahigh‐density unaggregated plasmonic Au nanoparticles (AuNPs) chemically bound to vertically aligned ZnO nanorod arrays (ZNA) through bifunctional molecular linkers. Experimental probes and electromagnetic simulations of electron transfer and localized plasmonic coupling processes are exploited to gain insight into the underlying light‐irradiation‐induced interactions in the 3D ZNA–AuNPs photocatalysts. Highly dense AuNPs on ZNA surfaces act as sinks for the storage of UV‐generated electrons, which promote the separation of charge carriers and create numerous photocatalytic reaction centers. Furthermore, 3D finite‐difference time domain simulation indicates that significant visible light confinement and enhancement around the ZNA–AuNPs interfacial plasmon “hot spots” contribute to efficient conversion of light energy to electron‐hole pairs. Significantly, in comparison with the bare ZNA, the 10‐nm‐sized AuNPs‐decorated ZNA exhibits 10.6‐fold enhanced photoreaction rate in the entire UV–vis region. Moreover, various novel hybrid structures based on the plasmonic AuNPs and diverse nanostructures (films, powdered nanorods, mesoporous, and nanotubes) or functional materials (multiferroic BiFeO₃, CuInGaSe₂ absorber layers, and photoactive TiO₂) are successfully constructed using the present synthesis methodology. It may stimulate the progress in materials science toward the synthesis of multifunctional plasmonic heterostructures or devices.     

可见光响应Fe3+-聚酰亚胺网络的合成及光诱导自由基聚合

将清洁、安全的太阳能(尤其是可见光)转化为化学能以合成高分子材料,一直是光催化领域的研究热点和难点.其关键问题是发展新型光催化材料,提升其在高分子合成环境下的光催化活性及稳定性.由于共轭微孔聚合物网络的独特优点,例如光电性能易调控、比表面积高以及结构相对稳定等,在光催化领域应用日益广泛.与其它共轭微孔聚合物网络相比,聚酰亚胺网络具有更高的光稳定性和耐化学腐蚀能力;同时,可用于合成聚酰亚胺网络的单体丰富,合成方法可靠,易于从分子层面调控其光电活性,提升其光催化活性.由于以上优点,基于聚酰亚胺网络的光催化体系在光诱导合成高分子材料领域展现出良好的应用前景.然而在实际应用中,聚酰亚胺网络却面临光催化活性不足的困扰.为解决此问题,本研究组曾设计,合成了以4,4',4'-三氨基三苯胺为核的聚酰亚胺网络,利用4,4',4'-三氨基三苯胺的给电子能力,促进聚酰亚胺网络中光生电子/空穴对的分离,有效提升了聚酰亚胺网络在可见光作用下对水相中有机污染物的光降解效率.在已有工作的基础上,本文设计、合成出一种新型聚酰亚胺网络,并通过配位作用,在聚酰亚胺网络网络中引入Fe^3+离子掺杂,提升其光催化性能,在有机环境中实现可见光诱导自由基聚合.首先,以三聚氰胺为电子给体单元,以1,4,5,8-萘四甲酸二酐为电子受体单元,通过酰亚胺缩聚反应构建出含电子给体-受体交替结构的聚酰亚胺网络(MPI);然后,通过浸渍法将Fe^3+离子引入到MPI网络内,制备出Fe^3+-聚酰亚胺网络(Fe@MPI).通过傅里叶变换红外光谱,粉末X射线衍射(XRD)和X射线光电子能谱对Fe@MPI的结构进行表征.结果显示,Fe^3+主要通过配位键的形式与MPI网络结合.同时,结合XRD谱图与扫描电子显微镜和透射电子显微镜结果可见,Fe^3+并非以氧化物或其它铁盐的形式简单地沉积在聚酰亚胺网络上,而是以Fe^3+-MPI配位作用均匀分布在MPI网络内.此外,XRD及氮气吸附实验结果表明,引入Fe^3+会破坏MPI网络的有序程度,导致复合材料的结晶度下降,但并不影响其多孔结构.通过紫外漫反射光谱和光电流谱对Fe@MPI的光吸收能力和光生电子/空穴对分离能力进行表征,结果显示,MPI网络与Fe^3+配位后,其光谱响应范围可拓宽至1250 nm,而其光电流响应强度也较纯MPI提升了3.5倍,表明引入Fe^3+配位可有效促进光生电子/空穴对的分离.基于其优异的光电性能,我们以Fe@MPI为光催化剂,在30℃下实现了甲基丙烯酸甲酯的可见光诱导自由基聚合,制备出分子量可达31.3×10^4 g mol^-1的聚甲基丙烯酸甲酯.同时,与MPI和FeCl3相比,Fe@MPI在相同条件下具有更高的催化效率,与其光电性能相吻合.最后,催化剂回收、循环实验表明,Fe@MPI易于回收,且具有良好的结构和性能稳定性:四次循环实验后,其结构和光催化活性均可基本保持不变.     

Porphyrinic covalent organic framework designed by molecular engineering as heterogeneous photocatalyst for aerobic mediated RAFT polymerization

Covalent organic frameworks (COFs) have gained increasing attention as heterogeneous materials for their prominent applications in photocatalytic processes. The already tailored structure endows COFs with ordered dimensional channels for the separation and migration of the electro-hole pairs and improves their photocatalytic properties. In this contribution, oxygen-mediated RAFT polymerization was achieved by using M-TCPP-DHTA-COFs (M = H₂ or Zn) as photocatalysts with the assistance of TEA as co-catalyst producing polymers with accurate molecular weight and narrow molecular weight distribution under visible light irradiation. The control experiments revealed excellent dual control behavior of light and gas toward polymerization processes. Notably, porphyrinic COFs can be straightforwardly separated and recycled for recycling experiments and exhibit remarkable compatibility features of controllable polymerization for functional monomers under aerobic conditions. This study offers a promising pathway for the construction of an efficient heterogeneous catalyst of oxygen-mediated RAFT polymerization and extends the novel applications of porphyrin-based COF materials.     

An efficient catalyst based on a water-soluble cobalt(II) complex of S,S′-bis(2-pyridylmethyl)-1,2-thiobenzene for electrochemical- and photochemical-driven hydrogen evolution

The reaction of S,S′-bis(2-pyridylmethyl)-1,2-thiobenzene and CoCl₂ affords a water-soluble cobalt(II) complex, [(bptb)CoCl₂], which has been characterized using various methods. Under blue light, together with CdS nanorods as a photosensitizer and ascorbic acid as a sacrificial electron donor, [(bptb)CoCl₂] can catalyze hydrogen generation from water and can work for 90 h. Under optimal conditions, this photocatalytic system achieves a turnover number (TON) of 22 900 moles of H₂ per mole of catalyst during 60 h of irradiation, and the highest apparent quantum yield is ca 26.63% at 469 nm. Moreover, [(bptb)CoCl₂] exhibits much higher activity than [(bpte)CoCl₂] (bpte = S,S′-bis(2-pyridylmethyl)-1,2-thioethane; TON = 6740 moles of H₂ per mole of catalyst during 60 h of irradiation), indicating that bptb can constitute a better catalyst for hydrogen production than bpte. This result can be attributed to the electronic properties of the ligands (bptb and bpte). The introduction of phenyl makes the electron distribution more uniform in the cobalt complex, allowing easier formation of the Co(III)–H species, further promoting the formation of hydrogen.     

Effects of the crystalline structure of Ga2O3 on the photocatalytic activity for CO production from CO2

Ga₂O₃ samples with different crystalline structures were prepared by calcination of a gallium nitrate powder around 800 K. Ga₂O₃ samples with mixed phases of γ and β showed high photocatalytic activity for CO production from CO₂ reduction with water, and the activity was even higher than that for an Ag-loaded β-Ga₂O_3. The photocatalytic activity increased with time. The increase was attributed to the appearance of GaOOH resulting from the interaction of Ga₂O₃ with water during the reaction as revealed by XRD and XPS analyses. In situ FT-IR measurements revealed that bicarbonates and bidentate carbonate species were adsorbed on GaOOH. Therefore, the increase of the photocatalytic activity with time would be derived from the formation of GaOOH phase on the γ-Ga₂O₃ and β-Ga₂O₃ sample.