硫取代氮增强g-C_(3)N_(4)光催化产氢性能

利用取之不尽的太阳能资源进行光催化水裂解制氢是缓解全球能源危机、实现碳中和战略的一项有前景的技术。石墨相氮化碳(g-C_(3)N_(4))因成本低且稳定性高在光催化产氢领域备受关注。然而,纯g-C_(3)N_(4)存在表面积小、电子转移慢、光生载流子复合快等缺陷,产氢性能通常不佳。本研究通过直接热解硫酸铵和三聚氰胺混合物,成功实现硫物种对g-C_(3)N_(4)氮位点的原位取代,开发出一种高效的硫掺杂g-C_(3)N_(4) (S-g-CN)光催化剂。系列结构和光谱表征证实硫的成功掺杂。密度泛函理论的第一性原理计算表明S活性位对氢的吸附吉布斯自由能近乎为零(~0.26 eV),揭示S掺杂在优化H活性中间体吸附和解吸过程中起着重要作用。透射电子显微镜和原子力显微镜测试结果表明,S-g-CN具有超薄的纳米片状结构,其片层厚度约为2.5 nm。随后的氮气吸脱附等温线和光电化学性质测试结果表明,S掺杂不仅可显著增大g-C_(3)N_(4)比表面积,而且还能有效提高其光生电子-空穴对的转移、分离和氧化还原能力。得益于材料良好的结构特性,S-g-CN的光催化产氢速率高达4923 μmol·g^(-1)·h^(-1),是原始g-C_(3)N_(4)的28倍,超越诸多最近报道的其它S掺杂g-C_(3)N_(4)光催化剂。而且,S-g-CN的表观量子效率高达3.64%。本研究除了开发一种高效的光催化剂,还将为高性能g-C_(3)N_(4)基催化剂的设计提供有益借鉴。

水蒸汽浴FeS_(2)高效Fenton降解甲草胺

由于硫化铁在自然环境中的丰富性,其生成活性氧和降解各种有机污染物的类Fenton活性已被广泛研究。然而,由于表面含铁活性位点的暴露有限,它们的类Fenton活性通常不高。在本研究中,以黄铁矿(FeS_(2))为例,基于水蒸汽对FeS_(2)的热处理,开发了一种提高硫化铁矿物Fenton活性的新策略,研究发现经水蒸汽热处理后的FeS_(2)(Heat-FeS_(2))对甲草胺(ACL)的非均相Fenton活性比由水热反应制备的母体FeS_(2)(Fresh-FeS_(2))更高。在初始pH为6.3时,Heat-FeS_(2)-Fenton体系对ACL的降解速率为0.48 min-1,约为Fresh-FeS_(2)-Fentton体系的23倍。电子自旋共振分析和苯甲酸探针实验证实,与Fresh-FeS_(2)-Fenton体系相比,在Heat-FeS_(2)-Fenton体系中产生更多的羟基自由基(·OH)和超氧自由基(·O_(2)^(-))。HeatFeS_(2)的Fenton活性大幅增强主要可归因于含量增加的高活性表面Fe^(2+)/Fe^(3+)组份、较高的Fe^(2+)浸出量和最佳的反应p H条件。扫描电镜,透射电镜,X射线光电子能谱(XPS)和傅里叶变换红外光谱等一系列表征结果表明,热处理可显著促进晶格Fe^(2+)向表面活性Fe^(2+)的转化,同时增强表面SO42-的生成,从而形成高酸性表面。此外,热处理后Fresh-FeS_(2)表面Fe^(2+)在表面总铁中的百分比从13%提高到了Heat-FeS_(2)的29%,而且Heat-FeS_(2)的Fe^(2+)浸出量(0.23 mmol·L-1)也远高于FreshFeS_(2)的Fe^(2+)浸出量(<0.02mmol·L-1)。为了进一步阐明Heat-FeS_(2)材料ACL降解活性增强的机理,我们通过XPS技术监测类Fenton反应前后Heat-FeS_(2)表面Fe和S物种的变化关系。结果表明,H2O_(2)反应后,Fresh-FeS_(2)和Heat-Fee S_(2)中Fe^(2+)和Fe^(3+)的表面含量显著增加,而S_(2)2-物种的表面浓度则相对下降,证实了S_(2)2-物种在Fe^(3+)还原为Fe^(2+)循环中的关键作用。重要的是,本研究不仅加深了对FeS_(2)氧化转化、腐蚀及其对天然环境中有毒有机物转化与降解的认识,而且还提供了一种基于硫化铁矿物的高效Fenton氧化方法。

Experimental and theoretical investigation of sulfur-doped g-C_(3)N_(4)nanosheets/FeCo_(2)O_(4)nanorods S-scheme heterojunction for photocatalytic H_(2)evolution

g-C_(3)N_(4)emerges as a promising metal-free semiconductor photocatalyst due to its cost-effectiveness,facile synthesis,suitable visible light response,and robust thermal stability.However,its practical application in photocatalytic hydrogen evolution reaction(HER)is impeded by rapid carrier recombination and limited light absorption capacity.In this study,we successfully develop a novel g-C_(3)N_(4)-based step-scheme(S-scheme)heterojunction comprising two-dimensional(2D)sulfur-doped g-C_(3)N_(4)nanosheets(SCN)and one-dimensional(1D)FeCo_(2)O_(4)nanorods(FeCo_(2)O_(4)),demonstrating enhanced photocatalytic HER activity.The engineered SCN/FeCo_(2)O_(4)S-scheme heterojunction features a well-defined 2D/1D heterogeneous interface facilitating directed interfacial electron transfer from FeCo_(2)O_(4)to SCN,driven by the lower Fermi level of SCN compared to FeCo_(2)O_(4).This establishment of electron-interacting 2D/1D S-scheme heterojunction not only facilitates the separation and migration of photogenerated carriers,but also enhances visible-light absorption and mitigates electron-hole pair recombination.Band structure analysis and density functional theory calculations corroborate that the carrier migration in the SCN/FeCo_(2)O_(4)photocatalyst adheres to a typical S-scheme heterojunction mechanism,effectively retaining highly reactive photogenerated electrons.Consequently,the optimized SCN/FeCo_(2)O_(4)heterojunction exhibits a substantially high hydrogen production rate of 6303.5μmol·g^(-1)·h^(-1)under visible light excitation,which is 2.4 times higher than that of the SCN.Furthermore,the conjecture of the S-scheme mechanism is confirmed by in situ XPS measurement.The 2D/1D S-scheme heterojunction established in this study provides valuable insights into the development of high-efficiency carbon-based catalysts for diverse energy conversion and storage applications.