NiS-PdS/CdS光催化剂的水热法合成及其可见光分解水产氢性能

为提高太阳能转化效率, 高效响应可见光的光催化剂的研究十分必要. 本研究以硫化镉、氯化钯、醋酸镍和硫脲为原料, 利用水热法制备了NiS-PdS/CdS复合光催化剂. 通过X射线衍射(XRD)、紫外-可见光漫反射光谱(DRS)、透射电子显微镜(TEM)和光致发光(PL)光谱等手段对光催化剂进行了表征, 并在乳酸牺牲剂中对光解水制氢活性进行了测试. 结果表明: 助催化剂NiS 和PdS 能较好地分布在CdS 表面上, 形成共负载的NiS-PdS/CdS 光催化剂, 其可见光下的活性比CdS明显增强, 当NiS 和PdS 负载量分别在1.5%和0.41%(w)时, NiS-PdS/CdS获得最好活性, 最大产氢量达到6556 μmol·h^-1, 是CdS活性的7倍, 是NiS/CdS的近3倍, 测得在λ=420 nm时的表观量子效率为47.5%. 助催化剂NiS 和PdS分别起到传递光生电子和光生空穴的作用,两者共负载相比于单独负载, 能使光生载流子的迁移和分离效率更高, 因此提高了光催化产氢活性.     

Carbonyl‐Grafted g‐C3N4 Porous Nanosheets for Efficient Photocatalytic Hydrogen Evolution

Carbonyl‐grafted g‐C₃N₄ porous nanosheets (COCNPNS) were fabricated by means of a two‐step thermal process using melamine and oxalic acid as starting reagents. The combination of melamine with oxalic acid to form a melamine–oxalic acid supramolecule as a precursor is key to synthesizing carbonyl‐grafted g‐C₃N₄. The bulk carbonyl‐grafted g‐C₃N₄ (COCN) was further thermally etched onto porous nanosheets by O₂ under air. In such a process, the carbonyl groups were partly removed and the obtained sample showed remarkably enhanced visible‐light harvesting and promoted the separation and transfer of photogenerated electrons and holes. With its unique porous structure and enhanced light‐harvesting capability, under visible‐light illumination (λ >420 nm) the prepared COCNPNS exhibited a superior photocatalytic hydrogen evolution rate of 83.6 μmol h⁻¹, which is 26 times that of the p‐CN obtained directly from thermal polycondensation of melamine.     

MOFs Conferred with Transient Metal Centers for Enhanced Photocatalytic Activity

Highly effective photocatalysts for the hydrogen‐evolution reaction were developed by conferring the linkers of NH₂‐MIL‐125(Ti), a metal–organic framework (MOF) constructed from TiO_x clusters and 2‐aminoterephthalic acid (linkers), with active copper centers. This design enables effective transfer of electrons from the linkers to the transient Cu²⁺/Cu⁺ centers, leading to 7000‐fold and 27‐fold increase of carrier density and lifetime of photogenerated charges, respectively, as well as high‐rate production of H₂ under visible‐light irradiation. This work provides a novel design of a photocatalyst for hydrogen evolution using non‐noble Cu²⁺/Cu⁺ as co‐catalysts.     

In situ integration of efficient photocatalyst Cu1.8S/ZnxCd1-xS heterojunction derived from a metal-organic framework

The development of photocatalysts for hydrogen evolution is a promising alternative to industrial hydrogen evolution; however, generation of high active, recyclable, inexpensive heterojunctions are still challenging. Herein, a novel strategy was developed to synthesize non-noble metal co-catalyst/solid solution heterojunctions using metal-organic frameworks (MOFs) as a precursor template. By adjusting the content of MOFs, a series of Cu_1.8S/Zn_xCd_1-xS heterojunctions were obtained, and the Cu_1.8S(3.7%)/Zn_0.35Cd_0.65S sample exhibits a maximum hydrogen evolution rate of 14.27 mmol h⁻¹ g⁻¹ with an apparent quantum yield of 3.7% at 420 nm under visible-light irradiation. Subsequently, the relationship between the heterojunction and photocatalytic activity were investigated by detailed characterizations and density functional theory (DFT) calculations, which reveal that loading Cu_1.8S can efficiently extend the light absorption, meanwhile, the electrons can efficiently transfer from Zn_0.35Cd_0.65S to Cu_1.8S, thus resulting more photogenerated electrons participating in surface reactions. This result can be valuable inspirations for the exploitation of advanced materials using rationally designed nanostructures for solar energy conversion.     

Energy-Saving Electrolytic Hydrogen Generation: Ni2P Nanoarray as a High-Performance Non-Noble-Metal Electrocatalyst

It is highly attractive but challenging to develop earth-abundant electrocatalysts for energy-saving electrolytic hydrogen generation. Herein, we report that Ni₂P nanoarrays grown in situ on nickel foam (Ni₂P/NF) behave as a durable high-performance non-noble-metal electrocatalyst for hydrazine oxidation reaction (HzOR) in alkaline media. The replacement of the sluggish anodic oxygen evolution reaction with such the more thermodynamically favorable HzOR enables energy-saving electrochemical hydrogen production with the use of Ni₂P/NF as a bifunctional catalyst for anodic HzOR and cathodic hydrogen evolution reaction. When operated at room temperature, this two-electrode electrolytic system drives 500 mA cm⁻² at a cell voltage as low as 1.0 V with strong long-term electrochemical durability and 100 % Faradaic efficiency for hydrogen evolution in 1.0 m KOH aqueous solution with 0.5 m hydrazine.     

Silver ferrite–graphene nanocomposite and its good photocatalytic performance in air and visible light for organic dye removal

Silver ferrite–graphene (AgFeO₂‐G) as a nanocomposite photocatalyst shows potent visible‐light photocatalytic activity for the degradation of organic contaminants, and generates the strong oxidants hydroxyl radical (^•OH) and superoxide anion radical (O₂^•−) via photoelectrochemical decomposition of H₂O and O₂ in the presence of air and visible light irradiation. The photogenerated electrons of AgFeO₂ can transfer easily from the conduction band to the reduced graphene oxide, efficiently preventing the direct recombination of electrons and holes. As a matter of fact, AgFeO₂ has a low bandgap. Furthermore, AgFeO₂ nanoparticles themselves have a magnetic property, which makes them magnetically separable. The experimental results show that the graphene nanosheets in the nanocomposite catalyst are exfoliated and decorated homogeneously with AgFeO₂ nanoparticles. The photodegradation occurs in a short time (ca 40 min). Also, the photocatalytic activity of the nanocomposite does not show any clear loss after ten recycles of the degradation process.     

Ag@AgCl修饰的锐钛矿相TiO2纳米管的制备及其光催化性能

首先采用水热合成法和双氧水处理制备了具有锐钛矿相的TiO2纳米管,然后通过沉淀和光化学反应将Ag@AgCl纳米粒子负载于其上,从而制得TiO2纳米管负载的表面等离子体光催化剂.结果表明,经Ag@AgCl纳米粒子修饰后,锐钛矿相TiO2纳米管因表面等离子共振效应而对可见光具有明显的响应,光生电子-空穴对更容易分离,因而T...     

Energy‐Saving Electrolytic Hydrogen Generation: Ni2P Nanoarray as a High‐Performance Non‐Noble‐Metal Electrocatalyst

It is highly attractive but challenging to develop earth‐abundant electrocatalysts for energy‐saving electrolytic hydrogen generation. Herein, we report that Ni₂P nanoarrays grown in situ on nickel foam (Ni₂P/NF) behave as a durable high‐performance non‐noble‐metal electrocatalyst for hydrazine oxidation reaction (HzOR) in alkaline media. The replacement of the sluggish anodic oxygen evolution reaction with such the more thermodynamically favorable HzOR enables energy‐saving electrochemical hydrogen production with the use of Ni₂P/NF as a bifunctional catalyst for anodic HzOR and cathodic hydrogen evolution reaction. When operated at room temperature, this two‐electrode electrolytic system drives 500 mA cm⁻² at a cell voltage as low as 1.0 V with strong long‐term electrochemical durability and 100 % Faradaic efficiency for hydrogen evolution in 1.0 m KOH aqueous solution with 0.5 m hydrazine.     

Integrating non-precious-metal cocatalyst Ni3N with g-C3N4 for enhanced photocatalytic H2 production in water under visible-light irradiation

Photocatalytic H₂ production via water splitting in a noble-metal-free photocatalytic system has attracted much attention in recent years. In this study, noble-metal-free Ni₃N was used as an active cocatalyst to enhance the activity of g-C₃N₄ for photocatalytic H₂ production under visible-light irradiation (λ > 420 nm). The characterization results indicated that Ni₃N nanoparticles were successfully loaded onto the g-C₃N₄, which accelerated the separation and transfer of photogenerated electrons and resulted in enhanced photocatalytic H₂ evolution under visible-light irradiation. The hydrogen evolution rate reached ～305.4 μmol h^?1 g^?1, which is about three times higher than that of pristine g-C₃N₄, and the apparent quantum yield (AQY) was ～0.45% at λ = 420. Furthermore, the Ni₃N/g-C₃N₄ photocatalyst showed no obvious decrease in the hydrogen production rate, even after five cycles under visible-light irradiation. Finally, a possible photocatalytic hydrogen evolution mechanism for the Ni₃N/g-C₃N₄ system is proposed.     

Enhanced photocatalytic activity of SiC modified by BiVO4 under visible light irradiation

SiC-BiVO₄-P and SiC-BiVO₄-H composites have been prepared by precipitation method and hydrothermal method, respectively. Rod-like BiVO₄ particles dispersed on the surface of micro-sized SiC particles homogeneously in SiC-BiVO₄-H. Due to the formed heterostructure between BiVO₄ and SiC, photo-generated electrons and holes were effectively separated. Under visible light irradiation, SiC-BiVO₄-H exhibited the best performance for photocatalytic oxidation of Rhodamine B, achieved about 7.5 times improvement in photocatalytic degradation rate constants compared with that of the pristine SiC powder. The possible photocatalysis mechanism of SiC/BiVO₄ related to the band positions of the semiconductors under visible light irradiation was also discussed in detail. In addition, the radicals trapping experiments revealed that all three radicals (holes, OH, and O₂^?) play an important role in the Rhodamine B degradation.     

Transition Metal Doping Induces Ti3+ to Promote the Performance of SrTiO3@TiO2 Visible Light Photocatalytic Reduction of CO2 to Prepare C1 Product.

Transition metal Fe, Co, Ni and Cu doped strontium titanate-rich SrTiO₃@TiO₂ (STO@T) materials were prepared by hydrothermal method. The prepared doped materials exhibit better photocatalytic CO₂ reduction to CH₄ ability under visible light conditions. Among them, Fe-doped and undoped SrTiO₃@TiO₂ under visible light conditions CO₂ reduction products only CO, while M-STO@T (M=Co, Ni, Cu) samples converted CO₂ to CH₄. The average methane yield of Ni-doped STO@T samples are as high as 73.85 μmol g⁻¹ h⁻¹. The production of methane is mainly due to the increase in the response of the doped samples to visible light. And the increase in the separation rate of photogenerated electrons and holes and the efficiency of electron transport caused by the generation of impurity levels. The impurity level caused by Ti³⁺ plays an important role in the production of methane by CO₂ visible light reduction. Ni doping effectively improves the photocatalytic performance of STO@T and CO₂ reduction mechanism were explained.     

Flexible Molecular Precursors for Selective Decomposition to Nickel Sulfide or Nickel Phosphide for Water Splitting and Supercapacitance

Herein, the synthesis of three nickel(II) dithiophosphonate complexes of the type [Ni{S₂P(OR)(4-C₆H₄OMe)}₂] [R=H ( 1 ), C₃H₇ ( 2 )] and [Ni{S₂P(OR)(4-C₆H₄OEt}₂] [R=(C₆H₅)₂CH ( 3 )] is described; their structures were confirmed by single-crystal X-ray studies. These complexes were subjected to surfactant/solvent reactions at 300 °C for one hour as flexible molecular precursors to prepare either nickel sulfide or nickel phosphide particles. The decomposition of complex 2 in tri-octylphosphine oxide/1-octadecene (TOPO/ODE), TOPO/tri-n-octylphosphine (TOP), hexadecylamine (HDA)/TOP, and HDA/ODE yielded hexagonal NiS, Ni₂P, Ni₅P₄, and rhombohedral NiS, respectively. Similarly, the decomposition of complex 1 in TOPO/TOP and HDA/TOP yielded hexagonal Ni₂P and Ni₅P₄, respectively, and that of complex 3 in similar solvents led to hexagonal Ni₅P₄, with TOP as the likely phosphorus provider. Hexagonal NiS was prepared from the solvent-less decomposition of complexes 1 and 2 at 400 °C. NiS (rhom) had the best specific supercapacitance of 2304 F g⁻¹ at a scan rate of 2 mV s⁻¹ followed by 1672 F g⁻¹ of Ni₂P (hex). Similarly, NiS (rhom) and Ni₂P (hex) showed the highest power and energy densities of 7.4 kW kg⁻¹ and 54.16 W kg⁻¹ as well as 6.3 kW kg⁻¹ and 44.7 W kg⁻¹, respectively. Ni₅P₄ (hex) had the lowest recorded overpotential of 350 mV at a current density of 50 mA cm⁻² among the samples tested for the oxygen evolution reaction (OER). NiS (hex) and Ni₅P₄ (hex) had the lowest overpotentials of 231 and 235 mV to achieve a current density of 50 mA cm⁻², respectively, in hydrogen evolution reaction (HER) examinations.     

Nanosized Metal Phosphides Embedded in Nitrogen‐Doped Porous Carbon Nanofibers for Enhanced Hydrogen Evolution at All pH Values

Transition‐metal phosphides (TMPs) have emerged as promising catalyst candidates for the hydrogen evolution reaction (HER). Although numerous methods have been investigated to obtain TMPs, most rely on traditional synthetic methods that produce materials that are inherently deficient with respect to electrical conductivity. An electrospinning‐based reduction approach is presented, which generates nickel phosphide nanoparticles in N‐doped porous carbon nanofibers (Ni₂P@NPCNFs) in situ. Ni₂P nanoparticles are protected from irreversible fusion and aggregation in subsequent high‐temperature pyrolysis. The resistivity of Ni₂P@NPCNFs (5.34 Ω cm) is greatly decreased by 10⁴ times compared to Ni₂P (>10⁴ Ω cm) because N‐doped carbon NFs are incorporated. As an electrocatalyst for HER, Ni₂P@NPCNFs reveal remarkable performance compared to other previously reported catalysts in acidic media. Additionally, it offers excellent catalytic ability and durability in both neutral and basic media. Encouraged by the excellent electrocatalytic performance of Ni₂P@NPCNFs, a series of pea‐like M_xP@NPCNFs, including Fe₂P@NPCNFs, Co₂P@NPCNFs, and Cu₃P@NPCNFs, were synthesized by the same method. Detailed characterization suggests that the newly developed method could render combinations of ultrafine metal phosphides with porous carbon accessible; thereby, extending opportunities in electrocatalytic applications.     

Reduced Graphene Oxide–Ag3PO4 Heterostructure: A Direct Z‐Scheme Photocatalyst for Augmented Photoreactivity and Stability

A visible light driven, direct Z‐scheme reduced graphene oxide–Ag₃PO₄ (RGO–Ag₃PO₄) heterostructure was synthesized by means of a simple one‐pot photoreduction route by varying the amount of RGO under visible light illumination. The reduction of graphene oxide (GO) and growth of Ag₃PO₄ took place simultaneously. The effect of the amount of RGO on the textural properties and photocatalytic activity of the heterostructure was investigated under visible light illumination. Furthermore, total organic carbon (TOC) analysis confirmed 97.1 % mineralization of organic dyes over RGO–Ag₃PO₄ in just five minutes under visible‐light illumination. The use of different quenchers in the photomineralization suggested the presence of hydroxyl radicals ( ^. OH), superoxide radicals ( ^. O₂^?), and holes (h⁺), which play a significant role in the mineralization of organic dyes. In addition to that, clean hydrogen fuel generation was also observed with excellent reusability. The 4 RGO–Ag₃PO₄ heterostructure has a high H₂ evolution rate of 3690 μmol h^?1 g^?1, which is 6.15 times higher than that of RGO.     

CdS Reinforced with CoSX/NiCo-LDH Core-shell Co-catalyst Demonstrate High Photocatalytic Hydrogen Evolution and Durability in Anhydrous Ethanol

At present, inefficient charge separation of single photocatalyst impedes the development of photocatalytic hydrogen evolution. In this work, the CoS_X/NiCo-LDH core-shell co-catalyst was cleverly designed, which exhibit high activity and high stability of hydrogen evolution in anhydrous ethanol system when coupled with CdS. Under visible light (λ≥420 nm) irradiation, the 3 %Co/NiCo/CdS composite photocatalyst exhibits a surprisingly high photocatalytic hydrogen evolution rate of 20.67 mmol g⁻¹ h⁻¹, which is 59 times than that of the original CdS. Continuous light for 20 h still showed good cycle stability. In addition, the 3 %Co/NiCo/CdS composite catalyst also shows good hydrogen evolution performance under the Na₂S/Na₂SO₃ and lactic acid system. The fluorescence (PL), ultraviolet-visible diffuse reflectance (UV-vis) and photoelectrochemical tests show that the coupling of CdS and CoS_X/NiCo-LDH not only accelerates the effective transfer of charges, but also greatly increases the absorption range of CdS to visible light. Therefore, the hydrogen evolution activity of the composite photocatalyst has been significantly improved. This work will provide new insights for the construction of new co-catalysts and the development of composite catalysts for hydrogen evolution in multiple systems.     

Ferroelectric Polarization Modulated Facet-selective Charge Separation in Bi4NbO8Cl Single Crystal for Boosting Visible-light Driven Bifunctional Water Splitting

Developing bifunctional water-splitting photocatalysts is meaningful, but challenged by the harsh requirements of specific-facet single crystals with spatially separated reactive sites and anisotropic charge transfer paths contributed by well-built charge driving force. Herein, tunable ferroelectric polarization is introduced in Bi₄NbO₈Cl single crystal nanosheets to strengthen the orthogonal charge transfer channels. By manipulating the in-plane polarization from octahedral off-centering of Nb⁵⁺ and out-of-plane polarization from lone pair electron effect of anisotropic Bi³⁺, both the fast charge recombination in bulk catalyst and the process of charge trapping into surface states can be effectively modulated. Collaborating with modest polarization electric field and facet junction induced built-in electric field, cooperative charge tractive force is constructed, which reinforces the spatial separation and migration of photogenerated electrons and holes to {110} reductive site facet and {001} oxidation site facet, respectively. While excessive polarization charges impair the facet-selective charge separation characteristics and conversely promote charge recombination on the surface. As a result, polarity-optimized Bi₄NbO₈Cl shows an excellent H₂ and O₂ evolution rate of 54.21 and 36.08 μmol ⋅ h⁻¹ in the presence of sacrificial reagents under visible light irradiation. This work unveils the function of ferroelectric polarization in tuning the intrinsic facet-selective charge transfer process of photocatalysts.     

Samarium and Nitrogen Co‐Doped Bi2WO6 Photocatalysts: Synergistic Effect of Sm3+/Sm2+ Redox Centers and N‐Doped Level for Enhancing Visible‐Light Photocatalytic Activity

Samarium and nitrogen co‐doped Bi₂WO₆ nanosheets were successfully synthesized by using a hydrothermal method. The crystal structures, morphology, elemental compositions, and optical properties of the prepared samples were investigated. The incorporation of samarium and nitrogen ions into Bi₂WO₆ was proved by X‐ray diffraction, energy dispersive X‐ray spectroscopy, and X‐ray photoelectron spectroscopy. UV/Vis diffuse reflectance spectroscopy indicated that the samarium and nitrogen co‐doped Bi₂WO₆ possessed strong visible‐light absorption. Remarkably, the samarium and nitrogen co‐doped Bi₂WO₆ exhibited higher photocatalytic activity than single‐doped and pure Bi₂WO₆ under visible‐light irradiation. Radical trapping experiments indicated that holes (h⁺) and superoxide radicals ( ^. O₂^?) were the main active species. The results of photoluminescence spectroscopy and photocurrent measurements demonstrated that the recombination rate of the photogenerated electrons and holes pairs was greatly depressed. The enhanced activity was attributed to the synergistic effect of the in‐built Sm³⁺/Sm²⁺ redox pair centers and the N‐doped level. The mechanism of the excellent photocatalytic activity of Sm‐N‐Bi₂WO₆ is also discussed.     

An EPR study of thermally and photochemically generated oxygen radicals on hydrated and dehydrated titania surfaces

The formation of a series of oxygen-centred radicals on different TiO₂ samples (P25 and two different rutile materials) under various conditions was investigated using X-band c.w. Electron Paramagnetic Resonance (EPR) spectroscopy. The radicals were formed either on thermally-reduced TiO₂, or by UV irradiation of the oxide under an oxygen atmosphere. The nature and stability of the radicals was also explored as a function of surface hydration. On thermally reduced TiO₂, containing surface and bulk Ti³⁺ centres, oxygen adsorption at 300 K results in the preferential formation and stabilisation of O₂ ^- anions on the P25 surface, but O^- and O₃ ^- anions are generated on the rutile surfaces. Superoxide anions (O^-) and trapped holes (O₂ ^-) were also identified after photo-irradiation of the thoroughly dehydrated TiO₂ samples under oxygen. The O^- anions were only visible at low temperatures under continuous irradiation, while the O₂ ^- anions were stable for days at 300 K. By comparison, on fully hydrated surfaces, no stable oxygen centred radicals could be detected on P25, while O₂ ^- anions were easily observed on the rutile surfaces. On partially hydrated P25, the O^-, O₂ ^- and HO₂ anions were detected after UV irradiation at 77 K; all radicals decayed upon warming to 298 K. On partially hydrated rutile, the O^- and O₂ ^- anions were detected and, unlike the case for P25, were found to be stable for days under the same conditions. The results illustrate the varied formation and stability of the oxygen centred radicals on TiO₂ surfaces depending on the pretreatment conditions.     

过硫酸盐激活协同可见光催化降解四环素的机理和降解路径

为了提升微污染水体中抗生素的降解效率,利用过硫酸钠（PDS）激活协同手性介孔TiO₂可见光催化（PDS/vis-TiO₂）对四环素（TC）进行降解。详细对比研究了以手性TiO₂作为催化剂的PDS激活（PDS/TiO₂）、可见光催化（vis-TiO₂）和PDS/vis-TiO₂三种体系中,降解污染物的活性物种和污染物降解路径等的差异。结果表明,不对称的螺旋堆积结构在手性介孔TiO₂中引入了丰富的Ti³⁺,不仅提升了其可见光响应,同时能够激活PDS生成自由基。PDS/vis-TiO₂体系中光生空穴h⁺和·OH等多种自由基可以同时参与TC的降解,5 h内其对TC去除率可达到95%以上,远超PDS/TiO₂体系（TC去除率为48.9%）和vis-TiO₂体系（TC去除率为71.1%）。PDS加入到光催化体系中,会受到光生电子的激活而产生自由基,从而消耗光生电子,提升光生空穴和电子的分离率,达到协同增强污染物的降解能力。另外PDS激活后产生自由基也会大大增加体系对TC的降解性能。密度泛函理论计算和中间产物分析结果表明,TC在PDS/vis-TiO₂体系中的降解路径包含了光生空穴h+攻击TC的降解路径,同时也包括自由基攻击TC的降解路径。     

CdBiO2Br nanosheets in situ strong coupling to carbonized polymer dots and improved photocatalytic activity for organic pollutants degradation

Carbonized polymer dots (CPDs) modified layer-structured CdBiO₂Br (CPDs/CdBiO₂Br) Z-scheme heterojunction hybrid material has been synthesized via simple solvothermal method. The hybrid material with Z-scheme heterojunction can effectively maintain the original highly oxidizing holes of CdBiO₂Br and the highly reducing electrons of CPDs. In addition, the construction of heterostructure is beneficial to the migration and separation of photogenerated carriers. Under visible light irradiation, 6 wt% CPDs/CdBiO₂Br showed the best catalytic activity for degradation of organic pollutants. Free radical capture experiments and ESR analysis confirmed that the main active species are ^?O₂^? and h⁺. The decomposition process of organic pollutants was analyzed by LC-MS. Finally, the probable visible light mechanism performance of CPDs/CdBiO₂Br as direct Z-scheme heterojunction photocatalytic materials was proposed.