Shuai Li,Shenghai Yang,Kangkang Li,Yanqing Lai,Chaoyong Deng,Changhong Wang
Graphical A green system for hafnium alkoxide synthesis was proposed. Simultaneous heterogeneous Hf dissolution and ethanol dehydrogenation followed by spontaneous solution-based binding of alkoxy with Hf 4+ ions gave Hf(OEt) 4 . After the optimum conditions – electrolyte, temperature, current densities, etc. – had been determined, a proof-of-concept experiment achieved waste-free production of Hf(OEt) 4 with high purity and yield. Besides the system‘s green credentials, it showed a high net profit of 30 477 USD per kg Hf(OEt) 4 and could be extended to the synthesis of other hafnium alkoxides. The conventional thermal method of preparing hafnium alkoxides [Hf(OR) 4 , R=alkyl] – excellent precursors for gate-dielectric HfO 2 on semiconductors – is severely hindered by its unsatisfactory environmental and economic burdens. Herein, we propose a promising electrodissolution-coupled Hf(OR) 4 synthesis (EHS) system for green and efficient electrosynthesis of Hf(OR) 4 . The operational principle of the electrically driven system consists of two simultaneous heterogeneous reactions of Hf dissolution and alcohol dehydrogenation, plus a spontaneous solution-based combination reaction. In applying ethanol as solvent and Hf metal as electrodissolution medium, we achieved waste-free production of high-purity hafnium ethoxide [Hf(OEt) 4 ] with an equivalent “a concomitant” reduction in CO 2 emission of 187.33 g CO 2 per kg Hf(OEt) 4 and a high net profit of 30 477 USD per kg Hf(OEt) 4 . This system is very competitive with the thermal process, which unavoidably releases substantial waste and CO 2 for a net profit of 27 700 USD per kg Hf(OEt) 4 . We anticipate that the environmental and economic benefits of the EHS process could pave the way for its practical application.
Currently, the conventional halide synthesis method of preparing hafnium alkoxides [Hf(OR) 4 , R is an alkyl] has problems of inefficiency, a heavy CO 2 emission footprint, and substantial solid and gas waste, which severely hinders its wide deployment. Herein, we propose an electrodissolution-coupled Hf(OR) 4 synthesis system using an alcohol solvent and Hf metal as feedstock for the efficient, low-carbon and waste-free electro-synthesis of Hf(OR) 4 . The electrochemical behavior of the tetraethylammonium-hydrogen sulfate (Et 4 NHSO 4 )-based EHS process is investigated by cyclic voltammetry, linear sweep voltammetry, Tafel, and electrochemical impedance spectroscopy, complemented with SEM observation. The anodic hafnium dissolution/corrosion occurs inside the passive film while the cathodic ethanol dehydrogenation occurs in a two-stage pathway. Tafel extrapolation and numerical fitting analysis acquires important kinetics parameters, such as corrosion current density, exchange current density, and apparent activation energy as well as solution, polarization and “Warburg” resistances, etc. This work can provide theoretical guidance for the efficient operation of EHS.
Copper is an attractive candidate for sensing ammonia. Here, an electrodissolution mechanism for measuring liquid-phase ammonia was developed via a novel three-dimensional rosette-like structure of copper nanoparticles (CuNPs) integrated onto carbon cloth (CuNPs/CC). A one-step hydrothermal synthetic procedure was employed to construct the metallic CuNPs with a stereo rosette-like pattern on flexible CC substrate. The morphology, composition and sensing performance of the as-prepared composite were characterised in detail. The CuNPs/CC composite showed excellent sensing performance to ammonia, which is attributed to the electrodissolution of CuNPs being promoted by ammonia to form a stabilised copper-ammonia complex. This electrochemical response occurs without the electro-oxidation of ammonia, thus avoiding the energy barrier of the N–N bond and the toxicity of N-adsorbates, which is advantageous for ammonia detection. In addition, the sensor also shows very high sensitivity to ammonia with a low detection limit, as well as good anti-interference performance, repeatability and stability. The high accuracy and precision for the quantification of ammonia concentration in a variety of real samples indicate that the CuNPs/CC composition has potential in the development of high-performance ammonia sensors.
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