Enhanced and Selective Photocatalytic reduction of CO2 by H2O over Strategically Doped Fe and Cr into Porous Boron Carbon Nitride
Strategic doping of metals and non-metals into a photocatalyst can help in tuning the band gap and alignment of band structure. Surface charge and charge transfer mechanism in a photocatalyst system govern the product amount and their distribution. Herein, we used wet-impregnation method to embed Fe and Cr into in-planes of porous boron carbon nitride and tested the photoactivity by reducing CO2 gas in the presence of water at room temperature under visible-light illumination. The total consumed electron number, a measure for photoactivity, was increased by 2.14 times for Cr-doped boron carbon nitride than that of the pristine graphitic carbon nitride. Also, selectivity for CO was increased with transition metal doping. X-ray photoelectron spectroscopy revealed that Fe existed in +2 and +3 oxidation states; while, Cr was in +3 and +6 states. Notably, optical and electronic properties were altered for the transition metal doped catalysts. Several in situ measurements were performed to identify reaction intermediates and underlying mechanism. COO- and HCHO were active intermediates for CO formation. And HCO3- could be an intermediate for CH4 generation. This work elucidates the pivotal role of trapped charge carriers in enhancing charge separation efficiencies and product selectivity. The results herein clearly demonstrate a promising strategy to use strong p-d repulsion between metal and non-metal elements on a host photocatalyst to extend the visible-light absorption range and reduce the recombination events, which can enhance selectivity and yields of products.