Multi-Walled Carbon Nanotubes Modified NiCo2S4 for the Efficient Photocatalytic Reduction of Hexavalent Chromium

Hexavalent chromium (Cr(VI)) compounds are considered to be occupational carcinogens, which can be transferred from the environment to the human body and pose a significant threat to human health. It is particularly urgent to explore a more efficient catalyst for removing Cr(VI) to comply with discharge standards. The addition of CNTs enables the separation and transfer of photogenerated charges. Thus, we synthesized a range of NiCo2S4 hybrid materials with different multi-walled carbon nanotube (MWCNTs) contents using a two-step hydrothermal method. The composites had significant advantages compared to pure NiCo2S4, such as an enhanced visible light absorption, increased specific surface area, high electron–hole pair separation, and fast electron transport. Thus, MWCNT addition enabled efficient photocatalytic performances in terms of reducing hexavalent chromium (Cr(VI)). Among all the composite samples, the MWCNT/NiCo2S4 with 0.050 g of MWCNTs achieved the highest efficiency in reducing Cr(VI) under light irradiation, which showed a removal rate close to 100% within 40 min. Such CNT-based composite photocatalysts could be used to reduce the highly toxic Cr(VI) in environmental applications.