金属碳化钨与液相染料光敏剂协同促进光催化制氢

Metallic Tungsten Carbide Coupled with Liquid-Phase Dye Photosensitizer for Efficient Photocatalytic Hydrogen Production

使用WC作为光催化材料通过水还原制氢很常见,但它通常需要与有效的光吸收剂协同才能产生有意义的光催化活性。这可归因于WC的窄带隙,导致水的氧化还原能力不足。有趣的是,我们的研究通过一种新型固液光催化体系克服了这种限制,该体系将裸WC光催化剂与液相光敏赤藓红B(Er B)相结合。这种概念的提出消除了将WC耦合到光吸收半导体的需要,这通常需要繁琐的程序来获得适当的功能化光催化复合材料。实验结果表明,在可见光(λ=520 nm)照射下,所提出的固液光催化体系产生了显著的氢气,然而,只有在三乙醇胺(TEOA)作为牺牲试剂的共同存在下。显然,仅加入WC和Er B的空白实验在典型的光催化条件下表现出几乎为零的光催化活性和无法测量的H_(2)生成。在光照TEOA溶液中仅存在Er B或WC的光反应中也观察到类似的活性。这些空白实验证实了所有三种成分的重要性,即WC、Er B和TEOA,它们分别作为光催化剂、光吸收剂和牺牲试剂,在我们提出的体系中产生有意义的H_(2)。值得注意的是,在我们的调查中系统地研究了三个关键参数,即p H值、Er B和WC浓度的影响。发现H_(2)生成的最佳p H值为8,稍微改变到更碱性或酸性条件会降低体系的光催化活性。在p H<8时,部分TEOA将发生部分质子化,从而失去其在光催化体系中作为牺牲试剂的活性。当p H值增加到超过8时,反应介质中的低质子浓度也会扰乱热力学驱动,导致体系产生的H_(2)受到抑制。同时,发现最佳Er B浓度为1mmol·L^(-1),从最佳点降低或增加Er B浓度均不利于H_(2)的产生。Er B浓度较低的体系(<1mmol·L^(-1)),在吸光上不足以满足体系的礼用,而较高浓度(>1 mmol·L^(-1)Er B)的体系,会引起明显的散射效应,组织光穿透反应溶液。相反,WC的浓度与H_(2)的生成呈稳定的正相关,在加入12 mmol·L^(-1)WC的体系中,H_(2)的生成量最高。在最佳条件下,成功生成了66μmol·h^(-1)H_(2),AQE略高为6.6%在520 nm处,这归因于Er B-TEOA-WC在所提出的体系中的协同作用。光电化学评估证实了Er B、TEOA和WC之间的相互作用,从而降低了阻抗,同时提高了体系中的电荷利用率。因此,还记录到了极好的H_(2)转换数(TON)为15,在至少20 h的连续反应中具有难以察觉的活性衰减。对于机理,密度泛函理论(DFT)计算进一步证实了W和C空位在H_(2)生成中的主要作用,这归因于他们提供的产品解吸,在光反应期间提高转化速率。从这些发现中得出结论,我们提出的新型WC/Er B/TEOA体系在液固光催化体系提供了一种更容易从水中产生H_(2)的策略,这为金属碳化物光催化剂避免选择繁琐的光吸收剂耦合。

Tungsten carbide(WC)is commonly used as a photocatalytic material for hydrogen production via water reduction.However,it is often combined with an effective photoabsorber to provide sufficient photoactivity.This is attributed to the narrow band gap of WC,which leads to an inadequate redox capability for water reduction.Notably,this limitation was overcome using a novel solid-liquid photocatalytic system that compliments bare WC photocatalysts with liquid-phase photosensitizing erythrosine B(ErB).The proposed concept eliminates the need to couple WC with photoabsorbing semiconductors,which often requires tedious procedures for the proper functionalization of photocatalytic composites.The experimental results indicated significant hydrogen production from the proposed solid-liquid photocatalytic system under irradiation with visible light(λ=520 nm);however,only in the presence of triethanolamine(TEOA)as a sacrificial reagent.Evidently,a blank experiment with only WC and ErB under typical photoreaction conditions exhibited nearly zero photoactivity and the production of H_(2)was undetected.Similarly,nonactivity was observed for the photoreaction in the presence of ErB or WC in the irradiated TEOA solution.These blank experiments confirmed the significance of all three components,namely WC,ErB,and TEOA,which functioned as the photocatalyst,photoabsorber,and sacrificial reagent,respectively,for suitable H_(2)production in the proposed system.The effects of three critical parameters,such as pH,ErB concentration,and WC concentration,were systematically investigated.The optimum pH for H_(2)production was 8,with a slight variation to more basic or acidic conditions reducing the photoactivity of the system.At pH<8,part of TEOA undergoes partial protonation,thereby losing its activity as a sacrificial reagent in the photocatalytic system.As the pH increased to>8,the low proton concentration in the reaction medium perturbed the thermodynamic drive,leading to suppressed H_(2)production.The optimum ErB concentration was 1 mmol·L^(-1),and decreasing or increasing the ErB concentration from the optimal point was detrimental to H_(2)production.The diluted system(ErB concentration<1 mmol·L^(-1))provided insufficient sensitizing agents,whereas the concentrated system(>1 mmol·L^(-1)ErB)induced significant scattering effects that prevent light from penetrating into the reactive liquid phase.Conversely,the WC concentration exhibited a positive correlation with H_(2)production in a steady manner,and the highest H_(2)production measured by the system was at a WC concentration of 12 mmol·L^(-1).Under optimum conditions,66μmol∙h^(-1)of H_(2)was successfully produced,with a slightly higher apparent quantum efficiency(AQE)of 6.6%at 520 nm,which was attributed to the synergism of ErB-TEOA-WC in the proposed system.The photoelectrochemical evaluation confirmed the positive interactions between ErB,TEOA,and WC,which caused reduced impedance while improving charge utilization in the system.Consequently,an excellent H_(2)turnover number(TON)of 15 was achieved with negligible activity decay for at least 20 h of reaction.Density functional theory(DFT)calculations confirmed the major roles of W-and C-vacant sites in H_(2)production,which were attributed to their enhanced product desorption that facilitates high turnover rates during photoreactions.In conclusion,the proposed novel liquid-solid photocatalytic WC/ErB/TEOA system provides more facile photo-derived H_(2)energy from water,which circumvents the tedious photoabsorber coupling of metal carbide photocatalysts.