CuNi bimetallic nanocatalyst enables sustainable direct carboxylation reactions

•Direct carboxylation of arenes using bimetallic CuNi nanocatalyst was explored.•Solvent-free, additive-free and activator-free conditions were involved.•Formic acid was used as carboxylating agent.•CuNi nanocatalyst is magnetically separable and recyclable.•The carboxylation mechanism involves C-H bond activation of benzene and formic acid.