In situ electrodeposition of nickel cobalt selenides on FTO as an efficient counter electrode for dye-sensitized solar cells

Construction of transition metal selenides with high electrocatalytic performance is of significant importance, but it is still a challenge to develop the corresponding counter electrodes (CEs) by an electrodeposition technique. In the present work, nickel cobalt selenide (Ni_xCo_ySe) films are prepared in situ on fluorine-doped tin oxide (FTO) glasses through a potential reversal electrodeposition technique. The morphology and electronic structure of Ni_xCo_ySe films can be tuned by controlling the Ni/Co molar ratio in electroplating solution. Specially, Ni_xCo_ySe-6 film (the Ni/Co molar ratio of 1:1) with the optimized interaction between the Ni and Co elements displays numerous particles composed of sheets attached with nanocrystals, resulting in the more electrocatalytic active sites. Benefiting from the unique morphology and optimized synergistic effect, Ni_xCo_ySe-6 CE exhibits superior electrocatalytic activity for the triiodide reduction. Then, the dye-sensitized solar cell (DSC) fabricated by Ni_xCo_ySe-6 CE has demonstrated a power conversion efficiency (PCE) over 7.40%, which is higher than that of platinum (Pt)-based device (6.32%). Furthermore, Ni_xCo_ySe-6 array CE is also prepared by using polystyrene array as template. The PCE of the DSC with Ni_xCo_ySe-6 array CE reaches its maximum value of 7.64% and 20.9% larger than that of Pt-based device.     

烟草秸秆低聚木糖的制备和纯化

为优化烟草秸秆低聚木糖制备参数,采用碱解方法提取木聚糖、酶解法制备低聚木糖以及单因素实验法考察了常见因素对工艺的影响。结果表明,木聚糖提取条件为：2.000 g秸秆粉末（≤100目）浸没于20.00 mL浓度为24% NaOH（m/V）和1% NaBH₄（m/V）碱液中,70 ℃条件下浸提4 h,滤液加3倍乙醇体积用量进行醇沉以及0.2倍乙酸体积用量进行中和。制备低聚木糖的条件为：溶液pH为5.50,温度40 ℃,时间6 h,木聚糖溶液（20 mg/mL）10 mL,木聚糖酶液（0.6%,m/V,4.1 U/mL）20 mL。低聚木糖分离提纯条件为：阳离子树脂柱分离纯化,填充高度18.0 cm、直径为4.5 cm;纯化液用高效液相色谱进行定性定量分析。通过上述方法得到的低聚木糖产品纯度较高,对工业制备低聚木糖工艺优化有一定的参考价值。     

A π-Conjugated Van der Waals Heterostructure Between Single-Atom Ni-Anchored Salphen-Based Covalent Organic Framework and Polymeric Carbon Nitride for High-Efficiency Interfacial Charge Separation

Semiconductor-based heterostructures have exhibited great promise as a photocatalyst to convert solar energy into sustainable chemical fuels, however, their solar-to-fuel efficiency is largely restricted by insufficient interfacial charge separation and limited catalytically active sites. Here the integration of high-efficiency interfacial charge separation and sufficient single-atom metal active sites in a 2D van der Waals (vdW) heterostructure between ultrathin polymeric carbon nitride (p-CN) and Ni-containing Salphen-based covalent organic framework (Ni-COF) nanosheets is illustrated. The results reveal a Ni N₂ O₂ chemical bonding in NiCOF nanosheets, leading to a highly separated single-atom Ni sites, which will function as the catalytically active sites to boost solar fuel production, as confirmed by X-ray absorption spectra and density functional theory calculations. Using ultrafast femtosecond transient adsorption (fs-TA) spectra, it shows that the vdW p-CN/Ni-COF heterostructure exhibits a faster decay lifetime of the exciton annihilation (τ = 18.3 ps) compared to that of neat p-CN (32.6 ps), illustrating an efficiently accelerated electron transfer across the vdW heterointerface from p-CN to Ni-COF, which thus allows more active electrons available to participate in the subsequent reduction reactions. The photocatalytic results offer a chemical fuel generation rate of 2.29 mmol g⁻¹ h⁻¹ for H₂ and 6.2 µmol g⁻¹ h⁻¹ for CO, ≈127 and three times higher than that of neat p-CN, respectively. This work provides new insights into the construction of a π-conjugated vdW heterostructure on promoting interfacial charge separation for high-efficiency photocatalysis.     

CoSe2 nanocrystals embedded into carbon support as coralline-like catalysts for hydrogen evolution reaction

It is vital to develop a high activity, stability and inexpensive hydrogen evolution reaction (HER) catalyst for electrochemical hydrogen evolution. A high-temperature reaction approach that is Co nanocrystals on carbon support (XC-72R) and selenylation to synthetize CoSe₂/C nanocrystals is used, and the effect of temperature on CoSe₂/C nanocrystals is studied. The morphology and catalytic properties of CoSe₂/C nanocrystals annealed at different temperatures are compared in 0.5 M H₂SO₄. The results indicated the coralline-like CoSe₂/C-650 nanocrystals have a high performance for HER with Tafel slopes of 45.73 mV·dec⁻¹ and onset potential of −196 mV vs. RHE. The stability maintained for at least 40 h and the Faraday Efficiency (FE) of H₂ is nearly 98%. The outstanding HER performance of CoSe₂/C-650 is due to its characteristic cora-like frame CoSe₂ nanocrystals embedded into supernal conductive XC-72R, which not only offer affluent active reaction sites, but also boost the capacity of charge transportation in HER process.     

低共熔溶剂中超疏水结构的一步电沉积制备及性能研究

目的 实现电沉积镀层表面微纳分级结构的简单构筑,赋予其优异的超疏水特性。方法 以氯化胆碱-尿素低共熔溶剂为溶剂,加入一定比例的氯化镍和硬脂酸溶解后得到电解液,通过调节电沉积时间得到一系列不同形貌的硬脂酸镍镀层。利用SEM、FTIR和XPS等表征技术研究了沉积时间对所制备镀层形貌和组成的影响,利用接触角测量仪探究了不同形貌硬脂酸镍的超疏水性和化学稳定性,利用电化学工作站考察了超疏水镀层的耐腐蚀性。结果 在低共熔溶剂中通过一步电沉积法得到不同形貌结构的硬脂酸镍镀层,其表面形貌与沉积时间密切相关。沉积初期呈现纳米片状结构,随着沉积进行,硬脂酸镍纳米片逐渐堆积、交叉,最终形成花状微纳分级结构。得益于其独特的微纳分级结构和自身低表面能特性,花状硬脂酸镍镀层不仅具有优异的超疏水性(θWCA=(157.3±1.9)°,θSA=(3.6±1.1)°)和自清洁特性,还对强酸、强碱以及盐溶液表现出优异的化学稳定性。与纳米片状和零散花状的硬脂酸镍相比,花状微纳分级结构的硬脂酸镍的耐腐蚀性(Jcorr=1.75×10⁻⁶ A/cm²)分别提高了20倍和7倍。结论 以低共熔溶剂为电解液,通过控制沉积时间可实现镀层表面微纳分级结构的调控与构筑,进而获得性能优异的超疏水镀层。     

Improved performance of surface functionalized TiO2/activated carbon for adsorption–photocatalytic reduction of Cr(VI) in aqueous solution

TiO₂ coated on activated carbon (TiO₂/AC) was synthesized by a facile sol-hydrothermal preparation. The as-prepared TiO₂/AC was modified by sequential treatment of nitric acid and thionyl chloride, followed by surface attaching of diethylenetriamine. The obtained materials were characterized by transmission electron microscopy, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, BET adsorption, and their adsorption–photocatalytic reduction activities were evaluated by the removal of aqueous Cr(VI). The results showed that TiO₂ particles were homogeneously deposited on the surface of activated carbon, and diethylenetriamine was grafted covalently onto the surface of TiO₂/AC through amide linkage. The diethylenetriamine-functionalized TiO₂/AC (TiO₂/AC-DETA) exhibits high adsorption capability for Cr(VI) through electrostatic, coordinative and hydrogen bonding interactions. The significant enhancement of photocatalytic activity of TiO₂/AC-DETA for reduction of Cr(VI) was observed, which was mainly attributed to the enrichment of Cr(VI) onto the surface of AC and successive fast interfacial transfer of Cr(VI) and photogenerated electrons resulted from the intimate contact between AC and TiO₂ through dense heterojunctions by forming of C–O–Ti linkages.     

Phase transitions and electrical characterizations of (K0.5Na0.5)2x(Sr0.6Ba0.4)5−xNb10O30 (KNSBN) ceramics with ‘unfilled’ and ‘filled’ tetragonal tungsten–bronze (TTB) crystal structure

Alkali-doped strontium barium niobate (K_0.5Na_0.5)_2x(Sr_0.6Ba_0.4)_5?xNb₁₀O₃₀ (KNSBN) ceramics has been prepared by a conventional solid-state reaction method. The alkali-dopant concentration x has been varied from 0.24 to 1.15 so that the crystal structure was transformed from ‘unfilled’ to ‘filled’ tetragonal tungsten–bronze (TTB) structure. Apart from the change in the structural properties, the effects of the alkali-dopants on the phase transition as well as ferroelectric, piezoelectric and pyroelectric properties have also been investigated. Phase transitions have been studied in the temperature range of ?200 °C to 350 °C. The origins of these phase transitions are discussed. The addition of the alkali-dopants enhances the ferroelectric, piezoelectric and pyroelectric properties of the KNSBN ceramics. Alkali-doping also favors abnormal grain growth and thus results in a porous microstructure, which might contribute to the enhancement of the pyroelectric performance.     

Oxygen-vacancy-rich Ag/Bi5O7Br nanosheets enable improved photocatalytic NO removal and oxygen evolution under visible light exposure

Photocatalytic NO removal is a green and sustainable alternative to the conventional thermocatalysis in the conversion of NO to nitrates. However, the efficiency of photocatalytic NO removal is restricted by weak NO adsorption and high charge recombination on photocatalyst. Herein, we report on one-step synthesis of Ag/Bi₅O₇Br nanosheets with rich oxygen vacancies (OVs) by a facile liquid phase reduction method. Under visible light irradiation on oxygen-vacancy-rich Ag/Bi₅O₇Br for 50 min the photocatalytic NO removal ratio is up to 64.65%, which is about 1.6 times higher than that by using pristine Bi₅O₇Br. The average oxygen production rate is 823 μmol·g^?1·h^?1, which is nearly 10 times higher than that of Bi₅O₇Br. Density functional theory (DFT) calculations reveal that OVs incorporation and plasmonic Ag can synergistically strengthen NO adsorption on Bi₅O₇Br. This work highlights the great potential of defects and plasmonic metals on synergistic enhancement in photocatalytic NO removal and oxygen evolution.     

π-Conjugated In-Plane Heterostructure Enables Long-Lived Shallow Trapping in Graphitic Carbon Nitride for Increased Photocatalytic Hydrogen Generation

The relatively short-lived excited states, such as the nascent electron–hole pairs (excitons) and the shallow trapping states, in semiconductor-based photocatalysts produce an exceptionally high charge carrier recombination rate, dominating a low solar-to-fuel performance. Here, a π-conjugated in-plane heterostructure between graphitic carbon nitride (g-CN) and carbon rings (C_rings) (labeling g-CN/C_rings) is effectively synthesized from the thermolysis of melamine–citric acid aggregates via a microwave-assisted heating process. The g-CN/C_rings in-plane heterostructure shows remarkably suppressed excited-state decay and increased charge carrier population in photocatalysis. Kinetics analysis from the femtosecond time-resolved transient absorption spectroscopy illustrates that the g-CN/C_rings π-conjugated heterostructure produces slower exciton annihilation (τ₁ = 7.9 ps) and longer shallow electron trapping (τ₂ = 407.1 ps) than pristine g-CN (τ₁ = 3.6 ps, τ₂ = 264.1 ps) owing to C_rings incorporation, both of which enable more photoinduced electrons to participate in the photocatalytic reactions, thereby realizing photoactivity enhancement. As a result, the photocatalytic activity exhibits an eightfold enhancement in visible-light-driven H₂ generation. This work provides a viable route of constructing π-conjugated in-plane heterostructures to suppress the excited-state decay and improve the photocatalytic performance.