Synthesis and characterization of the semiconductor Li0.93Cu0.07Nb3O8: Application to oxygen evolution under visible light

The semiconductor Li_0.93Cu_0.07Nb₃O₈ is prepared by soft chemistry in aqueous electrolyte via Cu²⁺ → Li⁺ exchange between copper nitrate and LiNb₃O₈. The substituted niobate crystallizes in an orthorhombic symmetry and the semiconducting and photo-electrochemical properties are investigated for the first time. The oxide exhibits a dark brown color and the UV–Visible spectroscopy gives an optical gap of 1.42 eV, due to the crystal field splitting of Cu²⁺ in octahedral site. The thermal variation of the conductivity shows that Nb: 4d-electrons are localized and the data are fitted by a small-polaron hopping model σ = σ_o exp {−0.053 eV/kT} with a carrier density thermally activated. The capacitance measurement done in ionic electrolyte (Na₂SO₄, 10⁻² M) indicates n type semiconductor with mixed valences Nb^5+/4+, due to the hetero-valent substitution Li⁺/Cu²⁺, with a flat band potential of 0.28 V_SCE and electrons density of 2.17×10¹⁷ cm⁻³. The Nyquist diagram shows mainly the bulk contribution with a diffusion process. The valence band (6.39 eV below vacuum) derives from O^2-: 2p orbital with a small admixture of Cu²⁺: 3d character while the conduction band is made up of Nb⁵⁺: 4d orbital. The material is successfully tested for the oxygen generation with an evolution rate of 87 µmol mn⁻¹ g⁻¹ under visible light (29 mW cm⁻²) and a quantum yield of 0.35%.     

Preparation and characterization of the brownmillerite Sr2Co2O5 as novel photocatalyst in the hydrogen generation

Sr₂Co₂O₅ is a semiconductor belonging to the brownmillerite family; it is prepared by nitrate route and the photo-electrochemical properties are assessed for the first time for the photocatalytic hydrogen production. Thermal analysis indicates the formation of the semiconductor phase at 750 °C. An optical transition at 1.10 eV, directly allowed is obtained from the diffuse reflectance spectrum, due to the internal Co³⁺: d-d transition in octahedral coordination. A flat band potential of 0.037 V_SCE is determined in KOH solution (0.1 M) from the Mott-Schottky characteristic and the results are relevant for the water reduction. The conduction band of Sr₂Co₂O₅ (−0.85 V_SCE), deriving from Co³⁺: 3d orbital is more cathodic than the potential of H₂O/H₂ couple and hydrogen is successfully evolved under visible light. A rate evolution of 68 µmol (g catalyst)⁻¹ min⁻¹ at pH ∼ 12 and a light-to-chemical energy efficiency of 0.82% are determined.     

Synthesis of micro-nano Ag3PO4/ZnFe2O4 with different organic additives and its enhanced photocatalytic activity under visible light irradiation

Several novel micro-nano Ag₃PO₄/ZnFe₂O₄ with excellent magnetic separation property and photocatalytic performance were successfully synthesized using different organic additives for the first time. In the composite, Ag₃PO₄ with flower-like, quadrangular prism and flake structures were obtained when the organic additive is hexadecyl trimethyl ammonium bromide (CTAB), sodium diethyldithiocarbamate (DDTC), or DL-malic acid (DLMA), respectively, while the ZnFe₂O₄ showed uniform spherical structure. From the results of the photocatalytic activity analysis, the Ag₃PO₄/ZnFe₂O₄ gained with the organic additive of DDTC showed the highest photocatalytic capability for 2, 4-dichlorophenol (2, 4-DCP) degradation under visible light irradiation compared with those of CTAB and DLMA as the additives. Moreover, the composition of the composite seriously influences the photocatalytic activity, and when the mass ratio of Ag₃PO₄ and ZnFe₂O₄ in the Ag₃PO₄/ZnFe₂O₄ (DITCH) is 9:1, the apparent photo degradation rate constant of 2, 4-DC is 0.0155 min⁻¹, which is 5.74 times of ZnFe₂O₄ (0.0027 min⁻¹) and 1.89 times of Ag₃PO₄ (0.0082 min⁻¹). Finally, the photocatalytic mechanism of Ag₃PO₄/ZnFe₂O₄ was discussed based on the heterojunction energy-band theory and Z-Scheme theory in detail.     

Synthesis and characterization of g-C3N4/BiFeO3 composites with an enhanced visible light photocatalytic activity

The novel visible light-induced g-C₃N₄/BiFeO₃ composites were successfully synthesized by introducing BiFeO₃ into polymeric g-C₃N₄. The structures and optical properties of composites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), field-emission transmission electron microscope (TEM), UV–vis diffuse reflection spectroscopy (DRS), respectively. For the degradation of Rhodamine B (RhB), the g-C₃N₄/BiFeO₃ composites exhibited significantly higher visible light photocatalytic activity than that of a single semiconductor. The optimal percentage of doped g-C₃N₄ was 50%. Both photooxidation and photoreduction processes follow first order kinetics. In addition, the stability of the prepared photocatalyst in the photocatalytic process was also investigated. The enhanced photocatalytic performance could be due to the high separation efficiency of the photogenerated electron–holes pairs. The possible photocatalytic mechanism of g-C₃N₄/BiFeO₃ was proposed to guide the further improvement of their photocatalytic activity.     

一种新型材料CH_3NH_3Pb_(0.5)Sn_(0.5)Br_3的制备与表征

采用溶液法制备一种新型有机无机杂化钙钛矿结构CH_3NH_3Pb_(0.5)Sn_(0.5)Br_3材料,采用X线衍射、热重分析、紫外可见光吸收、霍尔测试对其结构、稳定性、光电性能进行表征。结果表明,这种新型材料具有部分层状结构,在251.6℃下分解,同时光吸收范围在紫外和可见光范围,是一种p型半导体材料,载流子迁移率为63.1cm/V·s。     

工艺条件对KNNT陶瓷性能的影响

采用传统固相反应法制备了(K0.5Na0.5)(Nb0.7Ta0.3)O3(KNNT)无铅压电陶瓷。通过XRD、SEM分析方法分别研究了预烧后粉体和烧结后样品的晶体结构和微观形貌,以及预烧、烧结条件对样品性能的影响。结果表明,预烧后的粉体和烧结后的样品的晶体结构分别为四方相和斜方相;在860～920℃预烧,选择合适的烧结温度均可获得性能优异的陶瓷样品。较佳工艺条件为900℃预烧、1180℃烧结,样品d33可达到205pC/N,kp、k33分别为45.9%、60.5%。     

Electrochemical growth of tin(II) oxide films: Application in photocatalytic degradation of methylene blue

We have investigated the semiconducting and photoelectrochemical properties of SnO films grown potentiostatically on tin substrate. The oxide is characterized by X-ray diffraction, scanning electron microscopy and Raman spectroscopy. The anodic process corresponds to the formation of SnO·nH₂O pre-passive layer that is removed upon increasing potential due to surface etching at the metal/oxide interface. SnO films deposited for long durations (>50 mn) are uniform and well adhered; they thicken up to ~50 nm by diffusion-controlled process and the growth follows a direct logarithmic law. The thickness is determined by coulometry and the X-ray diffraction indicates the tetragonal SnO phase (SG: P4/mmm) with a crystallite size of 32 nm. The Mott–Schottky plot is characteristic of n type conductivity with an electrons density of 5.72×10¹⁸ cm⁻³, a flat band potential of −0.09 V_SCE and a depletion width of ~10 nm. The valence band, located at 5.91 eV below, vacuum is made up of hybridized O²⁻:2p Sn²⁺:5s while the conduction band (4.45 eV) derives from Sn²⁺:5p orbital. The electrochemical impedance spectroscopy (EIS) measured in the range (10⁻²–10⁵ Hz) shows the contribution of the bulk and grain boundaries. The energy band diagram predicts the photodegradation of methylene blue on SnO films. 67% of the initial concentration (10 mg L⁻¹) disappears after 3 h of exposure to visible light (9 mW cm⁻²) with a quantum yield of 0.072.     

Bi_(1.5)Zn_(1.0)Nb_(1.5)O_7/Ba_(0.5)Sr_(0.5)TiO_3复合薄膜介电性能的频率特性研究

采用射频磁控溅射法在蓝宝石基片上制备了Bi1.5Zn1.0Nb1.5O7(BZN)/Ba0.5Sr0.5TiO3(BST)双层复合薄膜,并研究了该薄膜在100 kHz~6 GHz频率范围内的介电性能。研究结果表明,BZN/BST复合薄膜的介电性能具有良好的频率稳定性。该复合薄膜的介电常数在研究的频率范围内基本与频率无关;其介电损耗在频率低于1 GHz时与频率无关,在频率高于1 GHz时随频率的上升而略微增大;薄膜在研究的频率范围内具有稳定的介电调谐率。     

CuAl_(1.6)Fe_(0.4)O_4/凹凸棒石复合材料的制备及可见光催化性能研究

采用溶胶-凝胶法制备了CuAl1.6Fe0.4O4尖晶石,以凹凸棒石(PG)为载体,合成了CuAl1.6Fe0.4O4/凹凸棒石复合材料。采用X射线粉末衍射(XRD)、扫描电镜(SEM)以及紫外-可见(UV-Vis)吸收光谱测试技术对样品的结构、形貌、吸光性能进行了表征和分析,同时以500W氙灯为光源,亚甲基蓝为降解对象,测试了其可见光催化活性,并详细考察了尖晶石负载量对其光催化性能的影响。实验结果表明,当尖晶石负载量为40%时,其可见光降解性能最佳,最佳降解率达到了98.55%。     

纳米Cu2O花的制备及其光学性质研究

以Cu(CH3COO)2.H2O为原料,CTMAB(十六烷基三甲基溴化铵)和NaOH为添加剂,NaBH4为还原剂,通过液相法在低温(60℃)的条件下分步合成了纳米Cu2O花。采用XRD、SEM、TEM和紫外–可见吸收光谱分析等手段对纳米Cu2O花进行了表征。结果表明,纳米Cu2O花的生长过程符合成核–溶解–再结晶的机制。对照实验发现,NaOH和CTMAB的浓度对最终纳米花的形成起了关键性的作用。     

0.8Na0.5Bi0.5TiO3-0.2K0.5Bi0.5TiO3复合掺杂铌酸钾钠压电陶瓷的结构及性能

采用液相包覆法制备了(1-x)(0.5NaNbO3-0.5KNbO3)-x(0.8Na0.5Bi0.5Ti03-0.2K0.5Bi0.5TiO3)(x=0,0.01,0.02,0.03,0.04,0.05)(KNN-BNKT)无铅压电陶瓷.研究了BNKT掺杂量x对KNN陶瓷的结构、介电、压电性能的影响.结果表明,制备的...     

Cu2O镂空材料的制备及其光催化性能研究

采用空气氧化法制备了六角状氧化亚铜的镂空结构。在空气中氧气的辅助下,液相还原法制备的形貌、尺寸均一的六角状氧化亚铜（Cu2O）可被原位镂空成鱼骨状结构。采用扫描电镜(SEM)、X线衍射(XRD)、透射电子显微镜（TEM）、比表面积测试（BET)、紫外 可见吸收（UV Vis）光谱等手段对Cu2O材料进行形貌、结构及催化性能表征。结果表明,六角状Cu2O沿{100}和{111}面逐步向内腐蚀镂空,在空气辅助腐蚀2 h后,材料的比表面积相比镂空前增加了90％。光催化实验结果表明,镂空Cu2O材料的光催化性能提高了30％。     

Fe_(81)Zr_7Nb_2B_(10)和Fe_(78)Co_(2.5)Zr_7Nb_2B_(10)Cu_(0.5)合金的热性能、微观结构及磁性能研究

采用单辊快淬法制备了Fe81Zr7Nb2B10和Fe78Co2.5Zr7Nb2B10Cu0.5非晶合金,在不同温度下对两种合金进行了热处理。利用差热分析仪(DTA)、X射线衍射仪(XRD)和振动样品磁强计(VSM)等仪器对两种合金的热性能、微观结构和磁性能进行了测试分析。结果表明在Fe78Co2.5Zr7Nb2B10Cu0.5合金的晶化过程中存在预结晶效应,而在Fe81Zr7Nb2B10合金的晶化过程中没有。Fe81Zr7Nb2B10和Fe78Co2.5Zr7Nb2B10Cu0.5合金经803 K退火后,分别有α-Fe和α-Fe(Co)相从非晶基体中析出。随退火温度的升高,两种合金的比饱和磁化强度(Ms)变化趋势相似,但矫顽力(Hc)变化趋势明显不同。     

Theoretical insight into the electronic and photocatalytic properties of Cu2O from a hybrid density functional theory

A comprehensive first-principle investigation, based on hybrid density functional theory, produces strong evidence that the Cu₂O band-edges do satisfy the requirements of the H⁺/H₂ and O₂/H₂O redox levels, demonstrating that it has enough driving force for photocatalytic overall water splitting. The calculated band gap of Cu₂O is 2.184 eV, which is consistent with the experimental value of 2.17 eV. The highly dispersive s–s hybrid states at the conduction band bottom result in a small effective mass of the electron, which is favorable to carrier separation and the carrier transfer to surface, and thus facilitate the reduction of H⁺ to H₂. The strong optical absorption of Cu₂O is beneficial to overall water splitting under visible light irradiation. Possible reasons for no observation of H₂ in some experiments are also discussed. The results address the ongoing controversy associated with photocatalytic overall water splitting of Cu₂O.     

Investigation of the ferroelectric properties of lead-modified Sr0.5Bao.5Nb2O6 with special reference to uncooled infrared detection

The physical and ferroelectric related properties of a Pb-modified SBN-50 (0.2 at.%) single crystal grown by the Czochralski method were investigated in some detail. The results of the measurements show that Pb-modified SBN has a relatively low dielectric constant, a high pyroelectric coefficient, and a favorable thermal and mechanical characteristics. The Curie temperature in comparison to pure SBN-50 was reduced from 121.0 to 116.7° C in the Pb-modified SBN. The calculated figures of merit based on the measured properties were compared with the unmodified SBN, La-modified SBN and the widely used LiTaO₃ single crystal. The results indicate that the Pb-modified SBN is a promising material for normal mode point detectors. The material has permanent bias to it’s polarization, so that infrared detectors made from this material can be operated over a wide range of temperature without being thermally depoled.     

BiCrO_3掺杂Na_(0.5)K_(0.5)NbO_3压电陶瓷的制备与性能

采用传统固相合成法制备了BiCrO3掺杂Na0.5K0.5NbO3无铅压电陶瓷。借助XRD、SEM等手段对该陶瓷的显微结构与电性能进行了研究。结果表明,当BiCrO3掺杂量为0.2%～1.0%(摩尔分数),样品均为ABO3型钙钛矿结构。当BiCrO3掺杂量为0.4%(摩尔分数)时,所得陶瓷样品具有最优综合电性能,其压电常数d33、机电耦合系数kp、机械品质因素Qm、斜方–四方相变温度tO-T和居里温度tC分别为138pC/N,0.32,30,175℃和410℃。     

La0.5Sr0.5CoO3的化学溶液淀积法制备与表征及其应用

采用化学溶液淀积法制备了具有纯钙钛矿结构和良好导电性能的La_(0.5)Sr_(0.5)CoO_3(LSCO)薄膜。LSCO的电阻率随着退火温度的升高、退火时间的增长和厚度增加而减小。650°C退火可以得到7mΩ·cm的电阻率。分别在LSCO和Pt衬底上制备了Bi_4Ti_3O_(12)(BTO)薄膜,分析结果表明,使用LSCO衬底对BTO的析晶有影响,击穿电压、铁电特性均有较大改善。     

Nb~(5+)/Ti~(4+)离子对O_3气敏元件的性能改善

在WO3中掺AN5+、Ti4+杂质离子,制成傍热式厚膜元件,结合开溢脱附（TPD）和半导体分析,研究了掺杂离子对元件性能的影响。