Current research on ZnFe2O4-based adsorbents rely mainly on its surface charge to remove Congo red (CR). However, the weak charge of ZnFe2O4 due its normal spinet structure makes this approach inefficient as evident from its low activity. Considering the potential of ZnFe2O4 as a low cost nontoxic adsorbent, it is important to improve its activity. Herein, we present an in-situ prepared 1-D ZnO-ZnFe2O4 with a heterojunction which adsorbs CR chemically instead of the generic physisorption. While its 1-D structure allows very low adsorbent loading to be employed. Together, these two unique properties make 1-D ZnO-ZnFe2O4 (similar to)3.3x more effective at treating CR effluent than reported ZnFe2O4-based adsorbents. The chemisorption reaction involves chelating/ bridging bidentate bonding between sulfonic groups on CR and ZnO-ZnFe2O4 heterojunction. Its potency is regulated by the ZnO content of the composite which suggest a synergistic effect between the metal oxides phases. Interestingly, spent 1-D ZnO-ZnFe2O4 can be regenerated in NaOH solution and retains (similar to)75% of its adsorption capacity even after repeated use. These findings provide key insights into how interfacial interactions in mixed metal oxide composites and their morphology affect dye adsorption. This information may be useful to develop high performing adsorbents from metal oxides in general.