Morphogenesis of Highly Uniform CoCO₃ Submicrometer Crystals and Their Conversion to Mesoporous Co₃O₄ for Gas-Sensing Applications

Abstract

Transition metal nitrates, carbonates, hydroxides, hydroxyoxides, and so forth are often used as solid precursors to synthesize their respective nanostructured metal-oxides after chemical/thermal conversion. However, synthesis of submicrometer uniform crystalline particles of this class of compound intermediates remains as a challenging but less studied area in nanomaterials research. In this work, we report a polyol process for controlled growth of cobalt carbonate (CoCO 3 ). A preparative investigation on morphogenesis of CoCO 3 crystals has been carried out, and three types of highly uniform CoCO 3 products (i.e., peanut-like, capsule-like, and rhombus crystals) in the submicrometer region have been synthesized at 200 °C under batch conditions. Uniform particles of tricobalt tetroxide (Co 3 O 4 ) have also been obtained at 300 °C from the CoCO 3 submicrometer crystals after thermal transformation in laboratory air. The Co 3 O 4 powder products possess mesoporosity and essentially preserve the pristine morphologies of their respective solid precursors. Due to high crystal uniformity and specific surface areas in the range of 140-149 m 2 /g, the mesoporous Co 3 O 4 exhibits enhanced performances for ethanol and carbon monoxide sensing.

Chemical Vapour Deposition of Gas Sensitive Metal Oxides

“…The p-type semiconductor titanium-doped chromium oxide (CTO) Cr 2´x Ti x O 3+y (0 ď x ď 0.4) shows very good selectivity and sensitivity towards NH 3 and H 2 S [70,71], with several techniques having been used to synthesize CTO gas sensing material including sol-gel [72][73][74][75][76], solid-state [77][78][79], solution [80,81] and CVD [82,83]. The synthesis of CTO powders, prepared via solid-state or sol-gel, and screen-printed onto an alumina sensor platform are the most widely used techniques but CTO has also been deposited using atmospheric pressure CVD (APCVD) using [CrO 2 4 ] as metal precursors [83,84].…”

“…Cobalt(II,III) oxide, Co 3 O 4 , is a magnetic p-type semiconductor most often used as a heterogeneous catalyst, in Li-ion batteries or as a solid-state sensor [80,[87][88][89]. CVD has been used to improve the sensor performance by homogenous doping with fluorine, with F-doped Co 3 O 4 successfully grown at temperatures between 200 and 400˝C by plasma enhanced-chemical vapour deposition using single-source precursors, Co(dbm) 2 (where dbm = 1,3-Diphenyl-1,3-propanedione) and Co(hfa) 2 TMEDA (where hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate and TMEDA = N,N,N',N'-tetramethylethylenediamine) respectively [90].…”

Tuning the Morphology of Metal Oxides for Catalytic Applications

“…Tricobalt tetraoxide (Co 3 O 4 ) is one of the most important magnetic p-type semiconductors and has been used in lithium-ion batteries, 54 chemical sensors, 55 and heterogeneous catalysis. [56][57][58][59][60][61][62][63] One prominent feature in these practical applications is that the performance of Co 3 O 4 is closely linked with its morphology.…”

High precision NH3 sensing using network nano-sheet Co3O4 arrays based sensor at room temperature

“…Among these, cobalt oxide, Co3O4, has received much research attention due to its high resistance to corrosion, abundant raw material and non-toxicity. It is a promising material for applications in Li-ion batteries [14][15][16], catalysts [17,18], and gas sensors [13,[19][20][21][22][23][24][25]. In particular, the oxidative catalytic activity of the Co3O4 is superior [17], thus it can be directly used to design or enhance the gas response, selectivity, and sensing kinetics [13,[19][20][21][22][23][24][25].…”

“…In particular, the oxidative catalytic activity of the Co3O4 is superior [17], thus it can be directly used to design or enhance the gas response, selectivity, and sensing kinetics [13,[19][20][21][22][23][24][25]. However, most reports on the Co3O4 sensors [13,[19][20][21]24,25] were focused on high temperature sensing applications (i.e., up to 300 o C). Up to now, the NH3 sensor based on the Co3O4 operated at room temperature has not been reported.…”