碳负载富氧空位的NiCo_(2)O_(4)用于电催化还原硝酸盐

Carbon-supported NiCoO with oxygen-rich vacancies for electrocatalytic reduction of nitrate

水体中硝酸盐是一种广泛存在的污染物,因此,开发用于水中硝酸盐还原的高效电催化剂受到广泛关注.采用溶胶-凝胶法耦合硼氢化钠还原法制备了碳负载富氧空位的NiCo_(2)O_(4-x)/C电催化剂,并研究其去除硝酸盐的性能.结果发现,在该体系中,耦合导电碳载体可改善半导体型电催化剂导电性,构建氧空位可促使原子H*生成,最终实现硝酸盐高效还原.NiCo_(2)O_(4-x)/C阴极在电流密度为20 mA·cm^(-2)、pH=7的条件下,可于3 h内去除水中94.8%的NO^(-)_(3)-N,相较于NiCo_(2)O_(4)及NiCo_(2)O_(4)/C阴极,NO^(-)_(3)-N去除率分别提高了36.6%和12.2%.此外,NiCo_(2)O_(4-x)/C阴极在连续5次还原硝酸盐过程中性能并未有明显变化.结合掩蔽实验和电子顺磁共振波谱分析证实,NiCo_(2)O_(4-x)/C阴极除了可通过直接电子还原硝酸盐外,还可以通过生成原子H*间接还原硝酸盐.通过对实际废水处理进一步验证其转化硝酸盐的性能,研究表明,NiCo_(2)O_(4-x)/C阴极可有效去除焦化废水生物出水中硝酸盐.

Nitrate is a ubiquitous pollutant in water.Developing efficient electrocatalysts for nitrate removal has attracted widespread attention.In this study;we used the sol-gel coupled with sodium borohydride reduction method to prepare carbon-supported NiCo_(2)O_(4)with oxygen-rich vacancies(NiCo_(2)O_(4-x)/C)electrocatalyst;and investigated its nitrate removal performance.In this system;the involvement of conductive carbon supports can improve the conductivity of semiconductor electrocatalysts;and the construction of oxygen vacancies can promote the generation of atomic H*;which ultimately render the obtained-catalyst attractive in electrochemical reduction of nitrate.The resulting NiCo_(2)O_(4-x)/C cathode removed 94.8%of NO^(-)_(3)-N in synthetic wastewater within 3 hours under the conditions of current density of 20 mA·cm^(-2)and pH=7.The removal rate increased by 36.6%and 12.2%in comparison to the NiCo_(2)O_(4)cathode and the NiCo_(2)O_(4)/C cathode;respectively.In addition;the performance of the NiCo_(2)O_(4-x)/C cathode towards nitrate reduction did not significantly change upon 5-cycle consecutive operation.The combination of the scavenger experiments and the electron paramagnetic resonance(EPR)measurements confirmed that the atomic H*-mediated indirect pathway also plays a significant role in nitrate reduction;in addition to the direct reduction pathway with respect to the NiCo_(2)O_(4-x)/C cathode.Testing with the real industrial wastewater further verified its potential application for nitrate conversion;as evident from the fact that the NiCo_(2)O_(4-x)/C cathode can effectively remove nitrate in the bio-treated coking wastewater(BTCW).