New tricks for an old dog: Visible light-driven hydrogen production from water catalyzed by fac-and mer-geometrical isomers of tris(thiosemicarbazide) cobalt(Ⅲ)

Increasing interest has been paid to the development of earth‐abundant metal complexes as promising surrogates of platinum for the electrocatalytically and photocatalytically driven hydrogen evolution reaction.In this work,we report on molecular H2‐evolving catalysts based on two octahedral complexes of cobalt thiosemicarbazide,fac‐[Co(Htsc)3]Cl3·3H2O(C1,Htsc=thiosemicarbazide)and mer‐[Co(Htsc)3]Cl3·4H2O(C2),which have facial(fac)and meridional(mer)geometry,respectively.Electrochemical studies confirmed that both C1and C2are active electrocatalysts in MeOH solution using acetic acid as the proton source,with the same overpotential of^640mV and TOF of^210s–1.The complex C1also exhibits electrocatalytic activity for hydrogen evolution reaction in aqueous media free of organic solvent with a moderate overpotential(560mV).Visible light‐driven hydrogen evolution experiments were carried out in combination with fluorescein as photosensitizer and triethylamine as sacrificial reductant in homogeneous environments.Our studies showed that both C1and C2can be used as efficient proton‐reduction catalysts in purely aqueous solution and have the same photocatalytic activities.A TOF of125h–1with a TON of900for photocatalytic H2generation using C1and C2in water were achieved for the noble‐metal‐free homogeneous system.It should be noted that this is the first reported study investigating the effect on the catalytic hydrogen production performance of using fac‐and mer‐isomers of molecular catalysts.

超高层转换层钢桁架施工关键技术

杭州西站项目超高层建筑转换层采用钢桁架型钢混凝土结构,其钢桁架施工质量对结构长期性能至关重要。为保障钢桁架施工精确控制,从三个方面开展钢桁架施工关键技术研究。首先,以钢结构分段重量、吊臂、吊重等为基本参数,通过分析吊重选择合适塔吊型号;理论分析堆载校核地下室顶板承载能力;基于四边简支双向板荷载分布影响,分析行车路线中地下室顶板最不利状态下承载能力,进而明确场地荷载部署,确保钢结构吊运能力满足要求。其次,通过建立钢结构三维模型将复杂结构可视化,检查封闭舱室判断浇筑施工难度。原方案中桁架层柱截面因多道腹板、横隔板交错形成了两层封闭舱室,且设计采用先封闭舱室注浆、后其他型钢混凝土结构统一浇筑的二次浇筑施工方法。基于深化的三维模型,以提高浇筑质量为原则,提出了钢柱横隔板顶面开设浇筑孔、内层舱室腹板开设流通孔,外层舱室不封闭而改为缀板连接,从而大大减小封闭空间;同时,基于扩大的横隔板孔洞,提出了改变混凝土流向的浇筑方案,以从上而下的一次性浇筑替代原有的先封闭压浆后支模浇筑的二次浇筑方案,优化钢结构构造保证浇筑成型。最后,结合塔吊吊装能力,设计桁架层施工安装流程。基于桁架安装流程,分析影响跨中变形影响因素;针对流程中关键参数跨中预拱度进行分析计算。胎架初始预设高度应由3部分位移组成,分别为有胎架支撑条件时半片桁架自重引起的跨中下挠、焊接完成拆除胎架后整体桁架因自重引起的跨中下挠和结构设计中考虑钢筋混凝土时设置的跨中预拱。采用ABAQUS建立三维实体非线性有限元模型,分别针对前述关键施工流程,计算考虑支撑刚度的施工状态下16.2 m跨径桁架层结构受力变形。结果显示:架设半侧桁架时,结构跨中挠度最大为6.41 mm;当拆除胎架后,结构跨中进一步下挠1.53 mm。为此,基于有限元计算结果,明确预拱值取值24.1 mm,约为跨径的1.5/1000。