Carbon-supported Sn–SnO₂ photocatalysts have been prepared for the first time using the newly designed dextran-mediated, epoxide-assisted sol–gel method. By coupling dextran with the epoxide assisted sol–gel technique we have established an easily modulated one-pot synthesis that demonstrates tunable carbon content with concerted production of a biphasic system. In effect, this method targets efficient development of photocatalysts that are metal-incorporated and catalyst-supported, very few methods such as this exist in the literature. This method eliminates traditional treatment steps required to create porous xerogels thereby eliminating days of processing. The formation of nanostructured sol–gels by epoxide-driven polycondensation was achieved using propylene oxide or glycidol, and the effects of the epoxide and dextran were explored in the formation of SnO₂ and Sn–SnO₂ carbon composite nanomaterial. The photocatalytic activity of selected SnO₂ and Sn–SnO₂ carbon composites were tested for the degradation of Rhodamine B (RhB). The biphasic systems show higher photocatalytic activity than the pure SnO₂ systems, a result of both increased heterojunction sites between metallic tin and tin oxide that lower recombination rates, in addition to the incorporation of a carbon network that displays increased dye adsorption. The original methods developed here should be further explored to access improved catalytic material.