Relatively large band-gap, fast charge carriers recombination, and mono-functionality of photocatalytic materials are still representing stumbling hurdles against their optimal usage for water cleaning. Herein, a novel black titanium oxide/plasmonic titanium nitride@activated coconut biochar (TiO 2-x /TiN@ACB) composite was designed to have both photocatalytic and photothermal functions. Intermediate states of black TiO 2-x , plasmonic effect of TiN, and high electrons (e−) capacity of biochar enhanced band-gap narrowing, light absorbance extension, and charge carriers separation respectively. Black TiO 2-x and plasmonic TiN sensitization via visible/infrared (Vis/IR) portion of photonic spectrum in addition to the confirmed close contact of composite constituents explained the demonstrated major role of e− in photocatalytic mechanism through efficient excitation and facile transfer. Thanks to black photocatalytic semiconductor and carbonic materials for their ultimate photons harnessing and efficient photothermal conversion where the composite exhibited a remarkable photothermal water evaporation upon Vis/IR illumination as well. TiO 2-x /TiN@ACB composite revealed 92.8 and 89.7% photocatalytic reduction of hexavalent chromium (Cr(VI)) and water evaporation efficiencies up to 92.9 and 51.1% upon IR and Vis light illumination respectively. This study proposes a new approach for efficient water cleaning by coupling of oxygen deficient and plasmonic semiconductors supported on naturally derived carbonic material as a broad spectrum harvester and bi-functional photocatalytic and photothermal material. [Display omitted] • Oxygen deficiency and plasmonic generation induced visible/infrared light response. • High electrons capacity of biochar enhanced charge carriers separation. • Major role of electrons in photocatalytic mechanism was exhibited. • Broad photonic range harnessing was beneficial for efficient photothermal conversion. • Synchronous photocatalytic and photothermal bi-functions have been achieved. [ABSTRACT FROM AUTHOR]