The correct answer to this open question is the following.
Blanche K. Bruce’s senatorship was different from that of Hiram Revels in that although Hiram Revels was the first African American in the United States Senate, he did not serve the entire six years term that is allowed for senators. The first African American Senator that indeed served his whole six years term was Blanche K. Bruce.
Hiram Revels entered the Senate after white Senator Albert G. Brown resigned in 1861. When Revels term ended he went to lead what today is Alcorn State University. In the case of Blanche K. Bruce, his term started in 1875 and ended in 1881. After his period he went to work for the US Treasury.