Synthesis of B4C powder via the carbothermal reduction and photoreduction of Cr(VI) on B4C under visible light irradiation

The environmental problem caused by wastewater containing hexavalent chromium (Cr(VI)) is of great interest and photocatalytic technology has recently been recognized as a suitable method for dealing with wastes containing Cr(VI). In this study, boron carbide (B4C) powders were synthesized through a carbothermal reduction process using a polymer precursor, polyvinyl borate (PVB), and boric acid. The synthesized B4C powders were studied as a photocatalyst for the removal of Cr(VI) from aqueous solutions under visible light irradiation. The effects of the B4C seed crystals and the Ni catalyst on the crystal purity as well as the Cr(VI) photoreduction efficiency of the prepared B4C powders were studied. B4C, synthesized in the presence of both the B4C seed crystals and the Ni catalyst, resulted in improved crystal purity, leading to an enhancement in the Cr(VI) photoreduction efficiency. The highest Cr(VI) removal rate of 65.1% was obtained. While the irradiation distance did not affect the Cr(VI) photoreduction efficiency much, the highest Cr(VI) removal was obtained with the visible light source (141 klux). The Cr(VI) removal rate was increased approximately 1.4 times with B4C powders synthesized in the presence of both the B4C seed crystals and the Ni catalyst. In addition, the effect of various parameters like the intial pH, Cr(VI) concentration and photocatalyst concentration on the Cr(VI) photoreduction efficiency of B4C was examined. Within the scope of examining the recyclability of the prepared photocatalyst, the Cr(VI) removal rate of B4C decreased from 65.1 to 52.4% after four consecutive cycles of Cr(VI) photoreduction experiments.