Mo掺杂调控电子结构增强NiS电催化固氮性能

以泡沫镍为骨架,通过水热法制备了Mo掺杂的NiS多级纳米花状结构(Mo-NiS)。在偏压为-0.7 V(vs RHE)下,2 h内,0.83 Mo-NiS(制备时钼、镍物质的量之比为0.83)的电催化固氮速率平均可达4.21μg·cm~(-2)·h~(-1),法拉第效率平均为18%。XPS测试和DFT计算表明,Mo掺杂增加了Ni活性位点周围的电子云密度,提高了电荷传输速率,促使*NNH_2到*N能垒大幅度降低,从而提升了电催化固氮效率。     

利用地球上丰富的炭黑和NiS_2双助催化剂修饰提高CdS纳米片体系的可见光产氢活性(英文)

光催化产氢技术是目前解决能源和环境问题的最有潜力的方法之一,因此制备安全高效的光催化剂已成为目前的研究热点.在目前研究的各种光催化剂中,CdS光催化剂因为具有较窄的带隙(2.4 eV)和合适的导带位置,所以在可见光催化产氢领域受到广泛关注.然而,光生电子/空穴对易复合和光腐蚀作用极大地限制了CdS光催化剂的放大应用.因此,人们采用众多改性策略以提高CdS光催化剂的可见光产氢活性,其中构建CdS纳米结构和负载助催化剂被认为是最有效的方式.构建CdS纳米结构既可以缩短载流子的迁移路径,也可以减少CdS晶体中的缺陷.很多不同纳米结构的CdS光催化剂已经被开发,例如纳米线、纳米颗粒和纳米棒等.因为制备过程极为复杂繁琐,所以CdS纳米片的研究鲜见报道.本文采用乙酸鎘和硫脲为原材料,通过简单的溶剂热法合成了CdS纳米片.在CdS的各类助催化剂中,由于常用的Pt,Ag和Au等贵金属的高成本和低储量等问题严重限制了它们的实际应用,所以近年来众多非贵金属助催化剂(例如MoS_2,WS2,NiS,NiO和WC等)得到了广泛关注.由于非贵金属助催化剂存在弱电导率和低功函数等问题,影响了对光生电子的收集和利用.纳米碳材料具有极高的电导率、强可见光吸收、有效的载流子分离和较多的反应位点等优点,因此组合纳米碳材料和非贵金属助催化剂被认为是一种有效的解决方案.本文首次采用炭黑和NiS_2作为双助催化剂改性CdS纳米片,通过简单的溶剂热/沉淀两步法成功合成了廉价高效的CdS/CB/NiS_2三元光催化体系.光催化产氢性能测试表明,CdS-0.5%CB-1%NiS_2展现出最高的光催化效率(166.7μmol h~(-1)),分别是CdS NSs和CdS-1.0%NiS_2的5.16和1.87倍.X射线衍射、高分辨电子显微镜和X射线光电子能谱结果证实了CdS催化剂的片状结构,且炭黑和NiS_2成功负载在CdS纳米片表面.紫外-可见漫反射结果表明,随着炭黑和NiS_2的负载,复合催化剂的吸收边缘产生明显的红移,且对可见光的吸收增强.荧光光谱、阻抗和瞬态光电流曲线测试结果证明,炭黑和NiS_2的加入可以有效地促进光生电子/空穴对分离.极化曲线结果表明,加入炭黑和NiS_2可以降低CdS的产氢过电势,因此加速表面产氢动力学.总之,炭黑和NiS_2之间显著的协同效应极大地提高了可见光吸收,促进光生电子/空穴对分离,加速表面产氢动力学,最终得到了三元光催化体系极高的光催化产氢活性.     

超薄骨架有序介孔CdS/NiS的制备及光催化产氢性能

采用有序介孔氧化硅为硬模板, 通过纳米浇筑法制备了由螺旋骨架构建的有序介孔硫化镉(CdS)光 催化材料. 该光催化材料具有约5 nm厚的超薄骨架和大的比表面积(238 m²/g), 能有效缩短光催化反应中 光生电荷迁移到表面进行反应的距离并同时提供更多的反应活性位点, 从而增强光催化性能. 通过原位化学沉积法将不同量的助催化剂硫化镍(NiS)沉积到有序介孔CdS表面, 得到了一系列超薄骨架有序介孔CdS/NiS复合光催化材料. 可见光照射下的光催化产氢活性测试结果表明, 负载适量NiS的有序介孔CdS具有显著增强的光催化产氢活性(3.84 mmol?h^-1?g^-1), 约为负载相同量NiS的普通商业化CdS材料(0.22 mmol?h^-1?g^-1)的17.5倍.     

NiS助催化剂的硫调控光沉积合成及其增强g-C3N4的光催化产氢性能

作为一种非金属聚合半导体,石墨相氮化碳(g-C3N4)具有特殊的能带结构、可见光响应能力以及优良的物理化学性质以及生产成本低等特点,因而已成为目前光催化领域的研究热点.然而,由于g-C3N4被光激发的电子与空穴极易复合,导致g-C3N4材料的光催化性能并不理想.而助剂修饰是实现光生载流子有效分离以提高光催化活性的有效途径.众所周知,贵金属Pt可以作为光催化产氢的反应位点,但高昂的成本限制了它的实际应用.所以,开发高效的非贵金属助剂很有必要.近年来,NiS作为优良的电子助剂在光催化领域受到广泛关注.大量研究表明,NiS可以作为g-C3N4的产氢活性位点用于提高其光催化产氢性能.NiS助剂主要是通过水热、煅烧和液相沉淀的方法修饰在g-C3N4的表面上.相较而言,助剂的光沉积方法具有一些独特的优势,例如节能、环保、简易并且能够实现其原位牢固地沉积在光催化剂的表面.然而g-C3N4光生电子和空穴强还原和氧化能力容易导致像Ni^2+的还原和S^2-的氧化等副反应发生,因此NiS助剂很难光沉积在g-C3N4材料表面.本文采用硫调控的光沉积法成功合成了NiS/g-C3N4光催化材料,该法利用g-C3N4在光照条件下产生的光生电子结合S以及Ni^2+生成NiS,然后原位沉积在g-C3N4表面.由于E0(S/NiS)(0.096 V)比E0(Ni^2+/Ni)(-0.23 V)更正,所以NiS优先原位沉积在g-C3N4表面.因此,硫调控的光沉积法促进了NiS的生成,并抑制了金属Ni等副反应的形成.通过X射线光电子能谱分析NiS/g-C3N4的表面化学态,表明该方法能成功地将NiS修饰在g-C3N4的表面,这也得到透射电镜和高分辨透射电镜结果的证实.光催化产氢的结果表明,NiS/g-C3N4光催化剂实现了良好的光催化性能,其最优产氢速率(244μmol h^?1 g^?1)接近于1 wt%Pt/g-C3N4(316μmol h^?1 g^?1).这是因为硫调控的光沉积法实现NiS助剂在g-C3N4表面的修饰,从而促进光生电子与空穴的有效分离,进而提高光催化制氢效率.此外,在该方法中,NiS的形成通常在g-C3N4光生电子的表面传输位点上,因此也能够使NiS提供更多的活性位点以提高界面产氢催化反应速率.电化学表征结果也进一步证明NiS/g-C3N4光催化剂加快了电子与空穴的分离和转移.更重要的是,这种简易且通用的方法还可以实现CoSx,CuSx,AgSx对g-C3N4的助剂修饰,并且都提高了g-C3N4的光催化产氢性能,表明该方法具有一定的普适性,为高效光催化材料的合成提供了新的思路.     

Laser-induced Fluorescence Spectroscopy of NiS: Identification of a Low-lying Electronic State

Laser-induced fluorescence excitation spectra of jet-cooled NiS molecules were recorded in the energy range of 12200-13550 cm^-1. Four vibronic bands with rotational structure have been observed and assigned to the [12.4]³∑₀^- -X³∑₀^- transition progression. The relevant rotational constants, significant isotopic shifts, and (equilibrium) molecular parameters have been determined. In addition, the lifetimes of the observed bands have also been measured.     

Laser-induced Fluorescence Excitation Spectrum of NiS in 15500-17200 cm^-1

The laser-induced fluorescence excitation spectrum of jet-cooled NiS molecule has been recorded in the energy range of 15500 17200 cm-1. Fifteen bands have been assigned as three transition progressions：[15.65]^3Ⅱ1（v′=0-4）-X^3∑0^-（v″=0）,[15.69]^3∑0^-（v′=0-4）-X^3∑0^-（v″=0）,and [15.81]^3Ⅱ1（v′=0-4）-X^3∑0^-（v″=0）.Spectroscopic constants for the three newly identified electronically excited states have been determined for the first time. In addition,the lifetimes for most observed vibronic bands have also been measured.     

An Efficient,Visible‐Light‐Driven,Hydrogen Evolution Catalyst NiS/ZnxCd1−xS Nanocrystal Derived from a Metal–Organic Framework

Photocatalytic water splitting for hydrogen production using sustainable sunlight is a promising alternative to industrial hydrogen production. However, the scarcity of highly active, recyclable, inexpensive photocatalysts impedes the development of photocatalytic hydrogen evolution reaction (HER) schemes. Herein, a metal–organic framework (MOF)‐template strategy was developed to prepare non‐noble metal co‐catalyst/solid solution heterojunction NiS/Zn_xCd_1−xS with superior photocatalytic HER activity. By adjusting the doping metal concentration in MOFs, the chemical compositions and band gaps of the heterojunctions can be fine‐tuned, and the light absorption capacity and photocatalytic activity were further optimized. NiS/Zn_0.5Cd_0.5S exhibits an optimal HER rate of 16.78 mmol g⁻¹ h⁻¹ and high stability and recyclability under visible‐light irradiation (λ>420 nm). Detailed characterizations and in‐depth DFT calculations reveal the relationship between the heterojunction and photocatalytic activity and confirm the importance of NiS in accelerating the water dissociation kinetics, which is a crucial factor for photocatalytic HER.     

Graphene oxides as support for the synthesis of nickel sulfide–indium oxide nanocomposites for photocatalytic,antibacterial and antioxidant performances

NiS (nickel sulfide)–In₂O₃ (indium oxide) nanostructures and NiS–In₂O₃ decorated on graphene oxide (GO) were demonstrated by ultrasonic/hydrothermal method. The structural study demonstrates the preparation of bixbyite and hexagonal phase of In₂O₃ and NiS for all of the synthesized catalysts. The band gap of the synthesized catalyst was determined to be in the range of 2.30–3.00 eV. A morphological evaluation by field emission scanning electron microscopy of NiS–In₂O₃ decorated on graphene oxide shows support for the NiS–In₂O₃ on the graphene oxide layer. Different test parameters were performed to study the phase and morphology. The particle sizes of the In₂O₃, NiS–In₂O₃ and NiS–In₂O₃/GO nanocomposites were 56.0, 62.0 and 66.0 nm, respectively. The photocatalytic performance of NiS–In₂O₃/GO nanocomposites was examined for the degradation of methylene blue dye under a UV lamp. The prepared sample shows 98.25% photocatalytic degradation within 40 min and at pH 9. With the presence the NiS and GO, the photo-degradation capacities of In₂O₃ and NiS–In₂O₃ are improved owing to the low band gap being calculated in UV–vis DRS analysis. The high ratio of NiS causes the highest photocatalytic properties of NiS–In₂O₃ nanocomposites owing to the enhancement of charge separation efficiency and generation of hydroxyl radicals. This study presents a facile and low-cost method to prepare highly active NiS–In₂O₃/GO nanocomposites. The antibacterial data indicate the significant properties of NiS–In₂O₃/GO nanocomposites for this study.     

Rational design of ternary NiS/CQDs/ZnIn2S4 nanocomposites as efficient noble-metal-free photocatalyst for hydrogen evolution under visible light

The NiS/CQDs nanocomposite (CQDs represents carbon quantum dots), with a mass ratio of NiS/CQDs to be 1.19:1 based on the ICP result, was obtained via a facile hydrothermal method from a mixture of CQDs, Ni(OAc)₂ and Na₂S. The self-assembly of ZnIn₂S₄ microspheres on the surface of NiS/CQDs was realized under microwave conditions to obtain a ternary NiS/CQDs/ZnIn₂S₄ nanocomposite. The as-obtained NiS/CQDs/ZnIn₂S₄ nanocomposite was fully characterized, and its photocatalytic hydrogen evolution under visible light irradiation was investigated. The ternary NiS/CQDs/ZnIn₂S₄ nanocomposite showed superior photocatalytic activity for hydrogen evolution than ternary CQDs/NiS/ZnIn₂S₄, which was obtained by deposition of NiS in the preformed CQDs/ZnIn₂S₄. The superior photocatalytic performance of ternary NiS/CQDs/ZnIn₂S₄ is ascribed to the introduction of CQDs, which act as a bridge to promote the vectorial transfer of photo-generated electrons from ZnIn₂S₄ to NiS. This result suggests that the rational design and fabrication of ternary CQDs-based systems are important for the efficient photocatalytic hydrogen evolution. This study provides a strategy for developing highly efficient noble-metal-free photocatalysts for hydrogen evolution using CQDs as a bridge to promote the charge transfer in the nanocomposite.     

Low-temperature heat capacities and thermodynamic properties of crystalline isoproturon

An incremental integral isoconversional method for the determination of activation energy as a function of the extent of conversion is presented. The method is based on the treatment of experimental data without their transformation so that the resulting values of activation parameters should not be biased. The method was tested for recovering the activation energies from simulated data and employed for the treatment of experimental data of the NiS recrystallisation. This revised version was published online in July 2006 with corrections to the Cover Date.