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Mixed-phase nanoTiO₂ materials attract a lot of attention as advanced photocatalysts for water decontamination due to their intrinsic structure that allows better photo-excited e⁻_cb-h⁺_vb charge separation, hence improved photocatalytic efficiency. Currently, the best-known mixed-phase TiO₂ photocatalyst is P25 with approximate composition 80% Anatase/20% Rutile (<b>A_/r</b>). Apart from Anatase (A) and Rutile (R) phases, there is Brookite (B) which has been evaluated less as photocatalyst in mixed-phase nanoTiO₂ systems. In this work we present a sustainable solution process to synthesize tunable composition mixed-phase nanotitania photocatalysts in a continuously stirred tank reactor (CSTR) by modulating conditions like pH, C_TiCl4 and time. In particular three mixed-phase TiO₂ nanomaterials were produced, namely one predominantly anatase with brookite as minor component (<b>A_/b</b>), one predominantly brookite with minor component rutile (<b>B_/r</b>), and one predominantly rutile with minor component brookite (<b>R_/b</b>) and evaluated as photocatalysts in the degradation of methyl orange. The three semiconducting nanomaterials were characterized by XRD and Raman spectroscopy to quantify the phase ratios and subjected to nano-morphological characterization by FE-SEM and TEM/HR-TEM. The new mixed-phase nanoTiO₂ materials are shown to be endowed with large specific surface area, ranging from 90–125 m² g⁻¹, double of that of P25, to be mesoporous and be surface-rich in Ti–OH molecular groups varying from 12%–20% versus 4% for P25. These properties though impact the adsorptive capacity with <b>R_/b</b> and <b>B_/r</b> removing > 50% of MO but not photocatalytic activity. The latter depends on nanograined mixed-phase structure and not mere assembly of different phase nanoparticles. First-order rate constants reveal essentially equivalent photocatalytic activity for anatase nanocrystals with either rutile (P25) or brookite (this work) domains.